Fix websocket error handing

Websockets have sockets, not responses.

Author: bfirsh

Diff for: lib/http-proxy/passes/ws-incoming.js

@@ -128,7 +128,7 @@ var passes = exports;
       if (clb) {
         clb(err);
       } else {
-        server.emit('error', err, req, res);
+        server.emit('error', err, req, socket);
       }
     }
   }