While I don't use this feature, there are developers who do. It's useful
when running migrations and changing branches.
I'm raising an `ActiveRecord::IrreversibleMigration` exception in every
`drop_table` migration because these migrations were all done before
version 1.0.0, and so making all of them reversible would be too much
work for little benefit.
DEPRECATION WARNING: Directly inheriting from ActiveRecord::Migration
is deprecated. Please specify the Rails release the migration was
written for:
class MigrationClass < ActiveRecord::Migration[4.2]
(called from require at bin/rails:4)