Allow for successful rollback of migration.

lib/generators/active_record/templates/migration.rb

@@ -1,8 +1,13 @@
 class TwoFactorAuthenticationAddTo<%= table_name.camelize %> < ActiveRecord::Migration
-  def change
+  def up
     change_table :<%= table_name %> do |t|
       t.string   :otp_secret_key
       t.integer  :second_factor_attempts_count, :default => 0
     end
   end
+
+  def down
+    remove_column :<%= table_name %>, :otp_secret_key
+    remove_column :<%= table_name %>, :second_factor_attempts_count
+  end
 end