Fullcalendar popover错误：引导工具提示需要Popper.js，尽管已经包含了该提示

Question

我试图在我的代码点火器应用程序的全日历中添加弹出窗口，但是，尽管提到的库已经明确包含在内，但我仍然收到以下错误：引导工具提示需要Popper.js。

这是我的JavaScript库的顺序：

  <!-- JS Libs -->

    <script src="https://code.jquery.com/jquery-3.3.1.js" integrity="sha256-2Kok7MbOyxpgUVvAk/HJ2jigOSYS2auK4Pfzbm7uH60=" crossorigin="anonymous"></script
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js" integrity="sha384-b/U6ypiBEHpOf/4+1nzFpr53nxSS+GLCkfwBdFNTxtclqqenISfwAzpKaMNFNmj4" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js" integrity="sha384-uefMccjFJAIv6A+rW+L4AHf99KvxDjWSu1z9VI8SKNVmz4sk7buKt/6v9KI65qnm" crossorigin="anonymous"></script>
    <script type="text/javascript" src="<?php echo base_url('assets/js/moment.js')?>"></script>
    <script type="text/javascript" src="<?php echo base_url('assets/fullcalendar-3.9.0/fullcalendar.js')?>"></script>

这是我的日历配置中的相关部分

eventRender: function(eventObj, $el) {
        $el.popover({
            title: eventObj.title,
            content: eventObj.description,
            trigger: 'hover',
            placement: 'top',
            container: 'body'
        });