Bootsrap 4下拉菜单没有显示？

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.6.0/dist/css/bootstrap.min.css">
<script src="https://cdn.jsdelivr.net/npm/bootstrap@4.6.0/dist/js/bootstrap.min.js"></script>

<div class="dropdown">
  <button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    下拉菜单
  </button>
  <div class="dropdown-menu" aria-labelledby="dropdownMenuButton">
    <a class="dropdown-item" href="#">菜单项1</a>
    <a class="dropdown-item" href="#">菜单项2</a>
    <a class="dropdown-item" href="#">菜单项3</a>
  </div>
</div>

$(document).ready(function(){
  $('.dropdown-toggle').dropdown();
});