With CRM2013 UR2 being released very soon I have made an update to the Ribbon Workbench that you'll be prompted to install by the auto update when you next open the Ribbon Workbench. I strongly advise you to install this update before you install UR2 otherwise the Ribbon Workbench will no longer work, and you'll need to re-download and re-install.
This is because when I updated the Ribbon Workbench for CRM2013 I retained the use of getServerUrl – the update now uses getClientUrl because UR2 has removed getServerUrl altogether.
getServerUrl was deprecated back in CRM2011 with UR12 so it's probably about time it was removed anyways!