Remove and ignore Gemfile.lock

Them gem itself doesn't need one, and test applications need to be bundled before tests can be run anyways.

Keeping a Gemfile.lock in the application directory means that the file will be updated whenever you run tests, and receive the version of the previous release if you're doing a new one. No point in doing that. :)

After removing all `Gemfile.lock`s, running `rake tests:bundle tests:run` still works and is all green. :green_heart: