Fixed issue with incorrect overlay positioning on iOS 8

Resolves #88
You need to account for the native scale when using native bounds, such as:

[UIScreen mainScreen].nativeBounds.size.width / [UIScreen mainScreen].nativeScale.
[UIScreen mainScreen].nativeBounds.size.height / [UIScreen mainScreen].nativeScale.

Otherwise, for iPads, while your location will be correct, your width won't be.