Bundling up Devise and its dependencies.

Among other things, Devise added the following dependencies to our
project.
    devise (3.1.0)
      bcrypt-ruby (~> 3.0)
      orm_adapter (~> 0.1)
      railties (>= 3.2.6, < 5)
      thread_safe (~> 0.1)
      warden (~> 1.2.3)

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