Merge pull request #580 from OneSignal/release-3.4.0

Release 3.4.0

Author: emawby

pubspec.yaml

@@ -1,6 +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: 3.3.2
+version: 3.4.0
 author: Brad Hesse <[email protected]>, Josh Kasten <[email protected]>
 homepage: https://github.com/OneSignal/OneSignal-Flutter-SDK