Remove Gemfile.lock

"When developing a gem, use the gemspec method in your Gemfile to avoid duplication. In
general, a gem’s Gemfile should contain the Rubygems source and a single gemspec line. Do
not check your Gemfile.lock into version control"

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