Fix an issue with Messaging needing a variable to be final

Author: a-maurice

messaging/src/android/java/com/google/firebase/messaging/cpp/RegistrationIntentService.java

@@ -38,7 +38,7 @@ public class RegistrationIntentService extends JobIntentService {
   // Fetch the latest registration token and notify the C++ layer.
   @Override
   protected void onHandleWork(Intent intent) {
-    Context context = this;
+    final Context context = this;
     FirebaseMessaging.getInstance().getToken()
       .addOnCompleteListener(new OnCompleteListener<String>() {
         @Override