[DOC beta] Fix the namespace of the Ember.getProperties method.

Previously it was incorrectly being rendered on the Ember.InjectedProperty page.

![screen shot 2014-12-30 at 10 30 19 am](https://cloud.githubusercontent.com/assets/54056/5579912/cf517750-900f-11e4-8a90-ceece6c6cf94.png)