Adding AdSupport framework dependency to plugin.xml

iOS build fails without linking the AdSupport framework.

Dependency was created by commit 36d01833142a09abd21c2fc788b0617df51f6397 in [PushNotificationManager.m](https://github.com/shaders/pushwoosh-phonegap-3.0-plugin/blob/36d01833142a09abd21c2fc788b0617df51f6397/src/ios/PushNotificationManager.m#L29)