fix serverError handle

@@ -13,7 +13,9 @@ const checkRefer = helpers.urlFormat('/3party/check', {refer: replaceKey});
  * 服务器错误
  * @return {[type]}
  */
-exports.serverError = (err = {}, req, res, next) => { // eslint-disable-line
+exports.serverError = (err, req, res, next) => { // eslint-disable-line
+  err = err || {};
+
   logger.error(`error at path: ${req.url}`);
   logger.error(`${req.url},${typeof err === 'object' ? JSON.stringify(err) : err}`);