update framework build to include arm64 arch

The framework that was included in the project was build using Xcode 5.0. In that version, the "Standard Architectures" which the push-library is configured for, does not include the "arm64" arch.

Apple had decided from Xcode 5.1 release inwards to change the "Standard Architectures"  to also include the arm64 architecture (understandable ASAP is better to avoid issues). More details can be found on the "Building" section on the [Xcode 5.1 release notes](https://developer.apple.com/library/mac/releasenotes/DeveloperTools/RN-Xcode/xc5_release_notes/xc5_release_notes.html#//apple_ref/doc/uid/TP40001051-CH2-SW2)

When building the framework on Xcode 5.0  we get:
Architectures in the fat file: /Release-iphoneuniversal/AeroGearPush.framework/AeroGearPush are: i386 armv7 armv7s

In contrast on Xcode 5.1 (see the arm64 and x86_64 be included):
Architectures in the fat file: /Release-iphoneuniversal/AeroGearPush.framework/AeroGearPush are: i386 x86_64 armv7 armv7s arm64