Fix Rails/ReversibleMigration cop for change_column (#30835)

db/migrate/20170609145826_remove_default_language_from_statuses.rb

@@ -1,7 +1,11 @@
 # frozen_string_literal: true
 
 class RemoveDefaultLanguageFromStatuses < ActiveRecord::Migration[5.1]
-  def change
+  def up
     change_column :statuses, :language, :string, default: nil, null: true
   end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
 end