fix export example error

Author: wenzhixin

extensions/export.html

@@ -44,11 +44,11 @@ <h1>Export</h1>
     var $table = $('#table');
     $(function () {
         $('#toolbar').find('select').change(function () {
-            $table.bootstrapTable('refreshOptions', {
+            $table.bootstrapTable('destroy').bootstrapTable({
                 exportDataType: $(this).val()
             });
         });
     })
 </script>
 </body>
-</html>
+</html>