Add '-Werror' for main build and suppress one deprecation warning

Author: wu-hui

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/AndroidConnectivityMonitor.java

@@ -84,6 +84,7 @@ public void run() {
           };
     } else {
       NetworkReceiver networkReceiver = new NetworkReceiver();
+      @SuppressWarnings("deprecation")
       IntentFilter networkIntentFilter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
       context.registerReceiver(networkReceiver, networkIntentFilter);
       unregisterRunnable =