Update PhabricatorRepositoryEditor.php

To fix the following error when trying to create a repo: 
[Wed Mar 26 18:28:26 2014] [error] [client 10.130.72.140] PHP Fatal error:  Undefined class constant 'TYPE_CREDENTIAL' in /var/lib/data/phabricator/src/applications/repository/editor/PhabricatorRepositoryEditor.php on line 321, referer: http://phabricator.example.com