make the adapter working in AMD and node environment

Make the **ember-mocha-adapter** running in three different environments -- AMD, Node, Browser.

I am not too sure that two lines below will work as expected

      Mocha.interfaces['ember-bdd'] = emberBdd;
      mocha.ui('ember-bdd');

Where is the lowercase `mocha` coming from (`Mocha` itself is from the `mocha.js`) ?