chore: update SDK version comment reference

Author: fadi-george

android/src/main/java/com/onesignal/flutter/OneSignalPlugin.java

@@ -23,7 +23,7 @@ private void init(Context context, BinaryMessenger messenger) {
         this.context = context;
         this.messenger = messenger;
         OneSignalWrapper.setSdkType("flutter");
-        // For 5.0.0, hard code to reflect SDK version
+        // Keep in sync with pubspec.yaml version
         OneSignalWrapper.setSdkVersion("050501");
 
         channel = new MethodChannel(messenger, "OneSignal");