[fix] Missing comma in #3677 breaks backend login

In https://github.com/joomla/joomla-cms/pull/3677 there is a missing comma that breaks the backend login.

![error_ra](https://cloud.githubusercontent.com/assets/1119272/3217880/1d01bc98-efe4-11e3-98cd-bdd17f0e961d.png)