perf: lazy instantiation uuidv4

@@ -145,15 +145,17 @@ app.use((req, res, next) => {
 
     // 独立的 UDID
     if (!req.cookies.udid || (req.yoho.isApp && req.query.udid)) {
-        let udid = uuid.v4();
+        let udid;
 
         if (req.yoho.isApp && req.query.udid) {
             udid = req.query.udid;
+        } else {
+            udid = uuid.v4();
         }
 
         res.cookie('udid', udid, {
             domain: 'yohobuy.com',
-            expires: new Date(Date.now() + 365 * 24 * 60 * 60 * 1000)
+            expires: new Date(Date.now() + 365 * 24 * 60 * 60 * 1000) // 1Year
         });
         req.cookies.udid = udid;
     }