提高jquery加载速率（有cdn就加载，没有就加载本地）

<!-- Adds google cdn reference -->

<script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script> 

<!-- Cdn fail refers to local library -->

<script type="text/javascript">

    if (typeof jQuery == 'undefined') {

        document.write(unescape("%3Cscript src='{%$rootpath%}js/jquery-3.2.1.min.js' type='text/javascript'%3E%3C/script%3E"));

    }

</script>