Update Gemfile.lock

I'm getting an error on Travis that looks like this:

    You are trying to install in deployment mode after changing your Gemfile.
    Run `bundle install` elsewhere and add the updated Gemfile.lock to version
    control.

    You have added to the Gemfile:
    * rspec-rails (< 3, >= 2.13.1)

    You have deleted from the Gemfile:
    * rspec-rails (< 3, >= 2.13.1)