fix ua detect bug. code review by LZF

@@ -92,7 +92,7 @@ function callpay(orderCode) {
 function isWXOpen() {
     var ua = window.navigator.userAgent.toLowerCase();
 
-    if (ua.match(/MicroMessenger/i) === 'micromessenger') {
+    if (ua.match(/MicroMessenger/i).toString() === 'micromessenger') {
         return true;
     } else {
         return false;