Cleanup migration

db/migrate/20160811172945_add_can_push_to_keys.rb

-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
 class AddCanPushToKeys < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
+  disable_ddl_transaction!
 
-  # Set this constant to true if this migration requires downtime.
   DOWNTIME = false
 
-  # When a migration requires downtime you **must** uncomment the following
-  # constant and define a short and easy to understand explanation as to why the
-  # migration requires downtime.
-  # DOWNTIME_REASON = ''
-
-  # When using the methods "add_concurrent_index" or "add_column_with_default"
-  # you must disable the use of transactions as these methods can not run in an
-  # existing transaction. When using "add_concurrent_index" make sure that this
-  # method is the _only_ method called in the migration, any other changes
-  # should go in a separate migration. This ensures that upon failure _only_ the
-  # index creation fails and can be retried or reverted easily.
-  #
-  disable_ddl_transaction!
-
-  def change
+  def up
     add_column_with_default(:keys, :can_push, :boolean, default: false, allow_null: false)
   end
+
+  def down
+    remove_column(:keys, :can_push)
+  end
 end