Fix uialertview specs

Turns out iOS 8 is changing the root `UIWindow` class to `_UIAlertControllerShimPresenterWindow` (a subclass of `UIWindow`) after an app shows a `UIAlertView` or `UIActionSheet`.

Displaying a `UIActionSheet` also no longer increments the window count in the app when displayed.

Boooo. :ghost: 

This PR fixes it and should fix a lot of branches that are failing right now in Travis when they pull these changes in.