如何使Bootstrap 3导航栏在导航栏折叠时从下拉菜单变为折叠？

<nav class="navbar navbar-default">
  <div class="container-fluid">
    <!-- 导航栏头部 -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar-collapse">
        <span class="sr-only">切换导航</span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="navbar-brand" href="#">Logo</a>
    </div>

    <!-- 导航栏内容 -->
    <div class="collapse navbar-collapse" id="navbar-collapse">
      <ul class="nav navbar-nav">
        <li class="active"><a href="#">首页</a></li>
        <li><a href="#">关于我们</a></li>
        <li><a href="#">产品</a></li>
        <li><a href="#">服务</a></li>
        <li><a href="#">联系我们</a></li>
      </ul>
    </div>
  </div>
</nav>