rails/strong_parameters — pull request #3 by lest (2012-03-20 19:12:57+00:00)
Title: add Gemfile.lock to .gitignore

http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/

Do not check your Gemfile.lock into version control, since it enforces precision that does not exist in the gem command, which is used to install gems in practice.