care for iOS 8 registration when running under that platform

done for [AGCORDOVA-25](https://issues.jboss.org/browse/AGCORDOVA-25)

tested on both iOS 7 and iOS 8 device with push-helloworld demo and successfully registered and able to receive notifications.

Note:
you need to specify this branch when testing to get this version of the plugin that is:

```cordova plugin add https://github.com/cvasilak/aerogear-pushplugin-cordova.git#AGCORDOVA-25```