Revert "modified .gitignore to add Gemfile.lock to repo"

This reverts commit e394ed522a3aade481b3a5315d7d060d65e3a35f.

Don't check in Gemfile.lock for a gem codebase.

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