兼容 statusCode 503 限流场景

@@ -194,7 +194,7 @@ exports.serverError = () => {
 
             return res.redirect(checkRefer.replace(replaceKey, req.protocol + '://' + req.get('host') + req.originalUrl));
 
-        } else if (err.code === 9999991 || err.code === 9999992) {
+        } else if (err.code === 9999991 || err.code === 9999992 || +err.statusCode === 503) {
             return _err510(req, res, 510, err);
         }