Update README.md

FIX: react native firevase url in documentation, as the package is updates now

Author: RinorDreshaj

README.md

@@ -724,7 +724,8 @@ In some case your application can be unreachable :
 - when the user kill the application
 - when it's in background since a long time (eg: after ~5mn the os will kill all connections).
 
-To be able to wake up your application to display the incoming call, you can use [https://github.com/ianlin/react-native-voip-push-notification](react-native-voip-push-notification) on iOS or BackgroundMessaging from [react-native-firebase](https://rnfirebase.io/docs/v5.x.x/messaging/receiving-messages#4)-(Optional)(Android-only)-Listen-for-FCM-messages-in-the-background).
+To be able to wake up your application to display the incoming call, you can use [https://github.com/ianlin/react-native-voip-push-notification](react-native-voip-push-notification) on iOS or BackgroundMessaging from [react-native-
+](https://rnfirebase.io/messaging/usage#receiving-messages)-(Optional)(Android-only)-Listen-for-FCM-messages-in-the-background).
 
 You have to send a push to your application, like with Firebase for Android and with a library supporting PushKit pushes for iOS.