fix 510 title

@@ -39,7 +39,7 @@ const _err510 = (req, res, code, err) => {
         page: 'error',
         title: '服务器繁忙 | Yoho!Buy有货 | 潮流购物逛不停',
         pageHeader: headerModel.setNav({
-            navTitle: '服务器繁忙请稍后重试！'
+            navTitle: err.message || '服务器繁忙请稍后重试！'
         }),
         pageFooter: true,
         isErr: true