[Fix] 修复一个BUG：websocket在发送ping包时出错将不会重连，导致后续每ping一次报一次错。

vnpy/api/websocket/WebsocketClient.py

@@ -191,6 +191,7 @@ class WebsocketClient(object):
                 et, ev, tb = sys.exc_info()
                 # todo: just log this, notifying user is not necessary
                 self.onError(et, ev, tb)
+                self._reconnect()
             for i in range(60):
                 if not self._active:
                     break