pushPlugin (fix): wrapping $broadcast in an $apply() statement scope fix

Myself and others noticed with my previous pull request that the notification payload would not update scope, for instance if you used it to do something similar to this:

```javascript
myApp.controller(function($scope) {
  $scope.messageArray = [];

  $scope.$on('pushNotificationReceived', function(event, notification) {
    $scope.messageArray.push(notification.payload);
  });
});
```

and had the messageArray ng-repeated in html.

This is (I think) because the notification is coming from outside of Angular - from cordova to be more precise - and without this extra code the digest would never happen to update bindings/watches.

Please also note I did not run `gulp`, I noticed that it would bring in some other code not related to my fix.