Getting Rid of Deprecation Warnings and Removing Gemfile.lock from Version Control

This looks like a pretty cool library. This could come in handy! Thanks for making it.

This pull request eliminates some deprecation warnings when running the tests with `bundle exec rake` by updating the Rake version. Note that I moved the reference to Rake from the Gemfile to the gemspec. I hope that's ok. My understanding is that the gemspec is a more appropriate place for listing dependencies.

Also, I removed the Gemfile.lock from version control. Yehuda Katz the creator of bundler has said that the Gemfile.lock should only be checked into Git for applications not libraries (like this project). He explains this here: http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/.