docs($injector): Reword `fn` param docs and link to DI information
fix(docs.js): handle empty deps array for plunkr/jsfiddle

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).