socket: fix Socket#ack

lib/socket.js

@@ -225,10 +225,11 @@ Socket.prototype.onevent = function(packet){
 /**
  * Produces an ack callback to emit with an event.
  *
+ * @param {Number} packet id
  * @api private
  */
 
-Socket.prototype.ack = function(){
+Socket.prototype.ack = function(id){
   var self = this;
   var sent = false;
   return function(){
@@ -237,6 +238,7 @@ Socket.prototype.ack = function(){
     var args = Array.prototype.slice.call(arguments);
     debug('sending ack %j', args);
     self.packet({
+      id: id,
       type: parser.ACK,
       data: args
     });