increasing browser compatibility by calling Promise['finally']

Calling Promise['finally'] should increase support for older browsers.

According to the [AngularJS documentation for $q](https://docs.angularjs.org/api/ng/service/$q#the-promise-api):
```
 *   Because `finally` is a reserved word in JavaScript and reserved keywords are not supported as
 *   property names by ES3, you'll need to invoke the method like `promise['finally'](callback)` to
 *   make your code IE8 and Android 2.x compatible.
```