Fix `Rails/ReversibleMigration` cop for `drop_table`

db/migrate/20170205175257_remove_devices.rb

@@ -1,7 +1,11 @@
 # frozen_string_literal: true
 
 class RemoveDevices < ActiveRecord::Migration[5.0]
-  def change
+  def up
     drop_table :devices if table_exists?(:devices)
   end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
 end