DEV: Add RubyGems as source

DEV: Add RubyGems as source

diff --git a/Gemfile b/Gemfile
index fc48edf..7da32ec 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+source 'https://rubygems.org'
+
 group :development do
   gem 'rubocop-discourse'
 end

GitHub sha: c9d3d390