Avoid a warning due to bug in Dart SDK

pkg/mdns/lib/src/native_protocol_client.dart

 // Copyright (c) 2015, the Fletch project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
 library mdns.src.native_protocol_client;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
 
@@ skipping 83 matching lines @@
     // Find all network interfaces with an IPv4 address.
     var interfaces =
         await NetworkInterface.list(type: InternetAddressType.IP_V4);
     for (NetworkInterface interface in interfaces) {
       // Create a socket for sending on each adapter.
       var socket = await RawDatagramSocket.bind(
           interface.addresses[0], mDnsPort, reuseAddress: true);
       _sockets.add(socket);
 
       // Join multicast on this interface.
-      _incoming.joinMulticast(mDnsAddress, interface);
+      (_incoming as dynamic).joinMulticast(mDnsAddress, interface);
     }
     _incoming.listen(_handleIncoming);
 
     _starting = false;
     _started = true;
   }
 
   void stop() {
     if (!_started) return;
     if (_starting) {
@@ skipping 43 matching lines @@
     if (event == RawSocketEvent.READ) {
       Datagram datagram = _incoming.receive();
       List<ResourceRecord> response = decodeMDnsResponse(datagram.data);
       if (response != null) {
         cache.updateRecords(response);
         _resolver.handleResponse(response);
       }
     }
   }
 }