Bundler for git source
You may know how to bundle install from git source.
gem 'page_number', git: "https://gist.github.com/123456789"
Bundler for GitHub/Gist source
How about GitHub/Gist source? Bundler has shorthands for GitHub/Gist.
gem "page_number", github: "user_name/repo_name"
gem "page_number", gist: "gist_id_123456789"