Run upgrade migrations automatically after upgrading to a version that requires migrations

[jgrau]

From https://github.com/charlotte-ruby/impressionist/pull/245:

It looks like there are a handful of better patterns for this. Either adding the migrations to the migration load path or copying them over via a generator. As this stands now, having a record of this in the repo I think is a win, but ideally we should wire up a way to make the upgrade process more streamlined.