Fixing pluralization

Ember's `Container#lookupFactory` was returning the rule function not `{default: function(){}}`, which was causing this to break.  I verified this with an acceptance test in this project

Please take a look at the code that overrides `#lookupFactory` in the unit test. I'm not 100% sure how you guys intended that to work, but I kind of hacked it together to simulate the behavior I was seeing in `Container#lookupFactory`