Feedback formatting

[JacobEvelyn]

I noticed that the feedback that's passed in to the Devise translation sometimes has a trailing period and sometimes does not. This appears to be due to the fact that sometimes we return a sentence and sometimes we use join(". ")—in the latter case the last item won't have a trailing period.

One quick fix would be to either remove the trailing period from line 44, or add one to line 46. But I'm also wondering if this change could instead use newlines instead of periods, as that appears to be what the default Rails/Devise behavior is for other password validations. Does that make sense?