Now that we require Ruby over `2.3`, we can replace the current
suggestion methods we have with tooling from the `did_you_mean` gem.

There is a small user visible change and this is that we now offer a
single suggestion for misspelled options. We are suggesting fixes during
generator invocation and during a mistyped rails server rack handler. In
both cases, if we don't make a proper prediction on the first match, we
won't do so in the second or third one, so in my mind, this is okay.