Execute Ember.uuid if it's a function

In Ember 1.7.0-beta.5, `Ember.uuid` is actually a function. Right now everywhere in our app (which is running `1.7.0-beta.5`) all of our translated strings have an id of `i18n-NaN`. This resolves the issue.
@jamesarosen thanks. Clearly got too hasty and needed more :coffee: