We forgot to do so in commit fc757428e, when we upgraded rubocop-rails.
In this upgrade, this rule was changed to include the `change_column`
method.
Just like we did in commit df959b74f, I'm raising an
`ActiveRecord::IrreversibleMigration` exception in migrations done
before version 1.0.0, since making all of them reversible would be too
much work for little benefit.
5b7a969964