thoughtbot/factory_girl_rails — pull request #72 by alup (2012-09-10 11:10:56+00:00)
Title: No need to version-control Gemfile.lock

References:
- http://stackoverflow.com/questions/4151495/should-gemfile-lock-be-included-in-gitignore
- http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/