Stop accidentally defining RSpec

See https://github.com/harvesthq/time-warp/pull/6 for more info.

That was out-of-date and included a huge diff due to the stuff that's now handled by https://github.com/harvesthq/time-warp/pull/13

The non-whitespace diff of that PR is pretty simple: https://github.com/harvesthq/time-warp/pull/6/files?w=1, and that's what's recreated here.

Credit given to the original author.

/cc @mrsimo @bjhess