Add frozen string literal comment to files.

Add frozen string literal comment to files.

diff --git a/Gemfile b/Gemfile
index 6ac5785..4ba4089 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 group :development do
diff --git a/bin/pull_translations.rb b/bin/pull_translations.rb
index 755a227..789ccaa 100755
--- a/bin/pull_translations.rb
+++ b/bin/pull_translations.rb
@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 # Usage:
 #   bundle install
diff --git a/plugin.rb b/plugin.rb
index 8dcae84..9c6fa86 100644
--- a/plugin.rb
+++ b/plugin.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # name: discourse-staff-notes
 # about: Gives the ability for staff members to attach notes to users
 # version: 0.0.2
diff --git a/spec/user_history_spec.rb b/spec/user_history_spec.rb
index 0d0fcab..7467ab9 100644
--- a/spec/user_history_spec.rb
+++ b/spec/user_history_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe UserHistory do
diff --git a/spec/user_warning_spec.rb b/spec/user_warning_spec.rb
index 5e51045..1f734fc 100644
--- a/spec/user_warning_spec.rb
+++ b/spec/user_warning_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe UserWarning do

GitHub sha: 104d5173