docs(docs.js): change to handle zero-length deps array in prepareDefaultAppModule

Change return value of docsApp.serviceFactory.prepareDefaultAppModule to include empty array `[]` instead of array containing one empty string element `['']`.

This will correct script.js for simple plunkr/jsfiddle examples such as [ngChecked](http://docs.angularjs.org/api/ng.directive:ngChecked).