Add frozen string literal to all the files (#405)

Add frozen string literal to all the files (#405)

diff --git a/Gemfile b/Gemfile
index a7a7a0e..d6d1038 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 # Specify your gem's dependencies in onebox.gemspec
diff --git a/Guardfile b/Guardfile
index 3efb874..f0cab6e 100644
--- a/Guardfile
+++ b/Guardfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 guard :rspec, cmd: 'bundle exec rspec' do
   watch(%r{^spec/.+_spec\.rb$})
   watch(%r{^lib/(.+)\.rb$})               { |m| "spec/lib/#{m[1]}_spec.rb" }
diff --git a/Rakefile b/Rakefile
index d461a1d..0be9dc1 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,4 +1,6 @@
 #!/usr/bin/env rake
+# frozen_string_literal: true
+
 require "rspec/core/rake_task"
 require 'bundler'
 
diff --git a/lib/onebox.rb b/lib/onebox.rb
index 97a2224..a955a07 100644
--- a/lib/onebox.rb
+++ b/lib/onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "openssl"
 require "open-uri"
 require "multi_json"
diff --git a/lib/onebox/engine.rb b/lib/onebox/engine.rb
index 6b5a25f..eda5767 100644
--- a/lib/onebox/engine.rb
+++ b/lib/onebox/engine.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     def self.included(object)
diff --git a/lib/onebox/engine/amazon_onebox.rb b/lib/onebox/engine/amazon_onebox.rb
index 00cc5d1..25b726d 100644
--- a/lib/onebox/engine/amazon_onebox.rb
+++ b/lib/onebox/engine/amazon_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'json'
 require "onebox/open_graph"
 
diff --git a/lib/onebox/engine/asciinema_onebox.rb b/lib/onebox/engine/asciinema_onebox.rb
index b7bb00a..a1fc1db 100644
--- a/lib/onebox/engine/asciinema_onebox.rb
+++ b/lib/onebox/engine/asciinema_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class AsciinemaOnebox
diff --git a/lib/onebox/engine/audio_onebox.rb b/lib/onebox/engine/audio_onebox.rb
index d181466..29e4d7f 100644
--- a/lib/onebox/engine/audio_onebox.rb
+++ b/lib/onebox/engine/audio_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class AudioOnebox
diff --git a/lib/onebox/engine/audioboom_onebox.rb b/lib/onebox/engine/audioboom_onebox.rb
index a692d68..f15b6b2 100644
--- a/lib/onebox/engine/audioboom_onebox.rb
+++ b/lib/onebox/engine/audioboom_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class AudioboomOnebox
diff --git a/lib/onebox/engine/bandcamp_onebox.rb b/lib/onebox/engine/bandcamp_onebox.rb
index 737cd92..7118b28 100644
--- a/lib/onebox/engine/bandcamp_onebox.rb
+++ b/lib/onebox/engine/bandcamp_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class BandCampOnebox
diff --git a/lib/onebox/engine/cloudapp_onebox.rb b/lib/onebox/engine/cloudapp_onebox.rb
index 3f14e41..be35a7e 100644
--- a/lib/onebox/engine/cloudapp_onebox.rb
+++ b/lib/onebox/engine/cloudapp_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class CloudAppOnebox
diff --git a/lib/onebox/engine/coub_onebox.rb b/lib/onebox/engine/coub_onebox.rb
index 6158685..2562fe8 100644
--- a/lib/onebox/engine/coub_onebox.rb
+++ b/lib/onebox/engine/coub_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class CoubOnebox
diff --git a/lib/onebox/engine/douban_onebox.rb b/lib/onebox/engine/douban_onebox.rb
index 7dbb6c9..ff83157 100644
--- a/lib/onebox/engine/douban_onebox.rb
+++ b/lib/onebox/engine/douban_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class DoubanOnebox
diff --git a/lib/onebox/engine/five_hundred_px_onebox.rb b/lib/onebox/engine/five_hundred_px_onebox.rb
index 0aa44e1..9311812 100644
--- a/lib/onebox/engine/five_hundred_px_onebox.rb
+++ b/lib/onebox/engine/five_hundred_px_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class FiveHundredPxOnebox
diff --git a/lib/onebox/engine/flickr_onebox.rb b/lib/onebox/engine/flickr_onebox.rb
index ee02d40..ea69d03 100644
--- a/lib/onebox/engine/flickr_onebox.rb
+++ b/lib/onebox/engine/flickr_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative './opengraph_image'
 
 module Onebox
diff --git a/lib/onebox/engine/flickr_shortened_onebox.rb b/lib/onebox/engine/flickr_shortened_onebox.rb
index 161ee20..1c12430 100644
--- a/lib/onebox/engine/flickr_shortened_onebox.rb
+++ b/lib/onebox/engine/flickr_shortened_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative './opengraph_image'
 
 module Onebox
diff --git a/lib/onebox/engine/gfycat_onebox.rb b/lib/onebox/engine/gfycat_onebox.rb
index 0777d31..e813d8d 100644
--- a/lib/onebox/engine/gfycat_onebox.rb
+++ b/lib/onebox/engine/gfycat_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GfycatOnebox
diff --git a/lib/onebox/engine/giphy_onebox.rb b/lib/onebox/engine/giphy_onebox.rb
index 668f684..c54b9b1 100644
--- a/lib/onebox/engine/giphy_onebox.rb
+++ b/lib/onebox/engine/giphy_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GiphyOnebox
diff --git a/lib/onebox/engine/github_blob_onebox.rb b/lib/onebox/engine/github_blob_onebox.rb
index 9b3934f..e4c51b3 100644
--- a/lib/onebox/engine/github_blob_onebox.rb
+++ b/lib/onebox/engine/github_blob_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../mixins/git_blob_onebox'
 
 module Onebox
diff --git a/lib/onebox/engine/github_commit_onebox.rb b/lib/onebox/engine/github_commit_onebox.rb
index 1246633..f7b79a9 100644
--- a/lib/onebox/engine/github_commit_onebox.rb
+++ b/lib/onebox/engine/github_commit_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GithubCommitOnebox
diff --git a/lib/onebox/engine/github_gist_onebox.rb b/lib/onebox/engine/github_gist_onebox.rb
index beec45e..e5e641d 100644
--- a/lib/onebox/engine/github_gist_onebox.rb
+++ b/lib/onebox/engine/github_gist_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GithubGistOnebox
diff --git a/lib/onebox/engine/github_issue_onebox.rb b/lib/onebox/engine/github_issue_onebox.rb
index 4159059..3ecd3a4 100644
--- a/lib/onebox/engine/github_issue_onebox.rb
+++ b/lib/onebox/engine/github_issue_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GithubIssueOnebox
diff --git a/lib/onebox/engine/github_pullrequest_onebox.rb b/lib/onebox/engine/github_pullrequest_onebox.rb
index fbeb652..902e512 100644
--- a/lib/onebox/engine/github_pullrequest_onebox.rb
+++ b/lib/onebox/engine/github_pullrequest_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GithubPullRequestOnebox
diff --git a/lib/onebox/engine/gitlab_blob_onebox.rb b/lib/onebox/engine/gitlab_blob_onebox.rb
index 60ed92a..c9cc22b 100644
--- a/lib/onebox/engine/gitlab_blob_onebox.rb
+++ b/lib/onebox/engine/gitlab_blob_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../mixins/git_blob_onebox'
 
 module Onebox
diff --git a/lib/onebox/engine/google_calendar_onebox.rb b/lib/onebox/engine/google_calendar_onebox.rb
index 1f6b782..2500c92 100644
--- a/lib/onebox/engine/google_calendar_onebox.rb
+++ b/lib/onebox/engine/google_calendar_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GoogleCalendarOnebox
diff --git a/lib/onebox/engine/google_docs_onebox.rb b/lib/onebox/engine/google_docs_onebox.rb
index 3579a16..b3ca4dc 100644
--- a/lib/onebox/engine/google_docs_onebox.rb
+++ b/lib/onebox/engine/google_docs_onebox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Onebox
   module Engine
     class GoogleDocsOnebox
diff --git a/lib/onebox/engine/google_drive_onebox.rb b/lib/onebox/engine/google_drive_onebox.rb

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GitHub sha: e898a89e