Address warning from static analysis

The author property is deprecated in favor of [verified publishers](https://dart.dev/tools/pub/publishing#create-verified-publisher).

Author: iAmWillShepherd

pubspec.yaml

@@ -1,7 +1,6 @@
 name: onesignal_flutter
 description: OneSignal is a free push notification service for mobile apps. This plugin makes it easy to integrate your flutter app with OneSignal
 version: 3.4.1
-author: Brad Hesse <brad@onesignal.com>, Josh Kasten <josh@onesignal.com>
 homepage: https://github.com/OneSignal/OneSignal-Flutter-SDK
 
 flutter: