Remove explicit variable `Ember` from module definition.

Latest versions of Ember don't export it as a module, but rather set it as a global variable. Irritating as that is, having the module definition with the argument `Ember` sets `Ember` to `undefined` in the module scope, which gives us errors like

> Uncaught TypeError: Cannot read property 'Handlebars' of undefined 

On **ehbs.js:128**. This fixes it.
Merge pull request #3 from gfarrell/master

Fix Ember variable being set to undefined by module definition (because ember.js doesn't return a module).