[fix] connection.socket -> socket for source of x-forwarded-for data

lib/node-http-proxy/http-proxy.js

@@ -130,7 +130,7 @@ HttpProxy.prototype.proxyRequest = function (req, res, buffer) {
   //
 
   if (this.enable.xforward && req.connection && req.socket) {
-    req.headers['x-forwarded-for']   = req.connection.remoteAddress || req.connection.socket.remoteAddress;
+    req.headers['x-forwarded-for']   = req.connection.remoteAddress || req.socket.remoteAddress;
     req.headers['x-forwarded-port']  = req.connection.remotePort || req.socket.remotePort;
     req.headers['x-forwarded-proto'] = req.connection.pair ? 'https' : 'http';
   }