Add missing import (FirebaseMessaging)

Author: Axel Vencatareddy

android/src/main/java/com/dieam/reactnativepushnotification/modules/RNPushNotification.java

@@ -25,6 +25,8 @@
 import java.util.Map;
 import java.util.Random;
 
+import com.google.firebase.messaging.FirebaseMessaging;
+
 public class RNPushNotification extends ReactContextBaseJavaModule implements ActivityEventListener {
     public static final String LOG_TAG = "RNPushNotification";// all logging should use this tag