fix(table): 修复 table 的浏览器兼容性问题 (#2850)

src/modules/table.js

@@ -2952,7 +2952,7 @@ layui.define(['lay', 'i18n', 'laytpl', 'laypage', 'form', 'util'], function(expo
     var that = this;
 
     that.unobserveResize();
-    for (const propName in that) {
+    for (var propName in that) {
       if(lay.hasOwn(that, propName) && propName !== 'config'){
         that[propName] = null;
       }