Removed and ignored the Gemfile.lock.

Gemfile.lock files shouldn't be tracked for Gem projects. See
http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
for more information on this topic.
Merge pull request #77 from olery/gemfile-lock

Removed and ignored the Gemfile.lock