update release version

Author: fadi-george

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: 5.3.4
+version: 5.4.0-beta-01
 homepage: https://github.com/OneSignal/OneSignal-Flutter-SDK
 
 flutter:
@@ -22,5 +22,5 @@ dev_dependencies:
     sdk: flutter
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
-  flutter: '>=1.10.0'
+  sdk: ">=2.12.0 <3.0.0"
+  flutter: ">=1.10.0"