Adding Gemfile.lock via bundle

> Bundler maintains a consistent environment for ruby applications. It
> tracks an application's code and the rubygems it needs to run, so
> that an application will always have the exact gems (and versions)
> that it needs to run.
http://bundler.io/

If you were working on a gem, instead of an application, you would not
check-in your Gemfile.lock.

The following commands were run:
$ bundle
$ git add Gemfile.lock