修改倒计时显示

@@ -122,6 +122,9 @@ Page({
         // let leftTime = 30;
         let timer = that.data.timer;
         if (leftTime > 0) {
+          that.setData({
+            timer: formatTimeByMin(leftTime, 'm:s')
+          });
           interval = setInterval(() => {
             leftTime = leftTime - 1;
             timer = formatTimeByMin(leftTime, 'm:s');