Fixed a ReferenceError thrown in _didClose

Error details :

[script_path]/node_modules/sockjs-client/lib/WebSocketTransport.js:103
      if (this.readyState !== WebSocketTransport.CONNECTING && that.readyState
                                                               ^
ReferenceError: that is not defined
    at WebSocketTransport._didClose ([script_path]/node_modules/sockjs-client/lib/WebSocketTransport.js:103:64)
    at WebSocketTransport.onData ([script_path]/node_modules/sockjs-client/lib/WebSocketTransport.js:73:23)
    at WebSocket.emit (events.js:98:17)
    at Receiver.self._receiver.ontext ([script_path]/node_modules/ws/lib/WebSocket.js:682:10)
    at Receiver.opcodes.1.finish ([script_path]/node_modules/ws/lib/Receiver.js:391:14)
    at Receiver.expectHandler ([script_path]/node_modules/ws/lib/Receiver.js:378:31)
    at Receiver.add ([script_path]/node_modules/ws/lib/Receiver.js:87:24)
    at Socket.firstHandler ([script_path]/node_modules/ws/lib/WebSocket.js:663:22)
    at Socket.emit (events.js:95:17)
    at Socket.<anonymous> (_stream_readable.js:764:14)