Bootstrap 4 External Link on navbar not functioning

I'm trying to include these links on my Bootstrap 4 nav bar but they aren't clickable I've tried quite a few things but having no luck? Any suggestions?

    <!-- Navigation -->
<nav class="navbar navbar-expand-lg navbar-dark bg-dark fixed-top">
  <div class="container">
    <a class="navbar-brand" href="#">Zak Ng</a>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false" aria-label="Toggle navigation">
      <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse" id="navbarResponsive">
      <ul class="navbar-nav ml-auto">
        <li class="nav-item">
          <a class="nav-link" href="#">Home
            <span class="sr-only">(current)</span>
          </a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">Skills</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">Projects</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">Contact</a>
        </li>   

          <li class="nav-link"><a href="https://github.com/" target="_blank" class="fab fa-github-square fa-2x" aria-hidden="true"></a></li>
          <li class="nav-link"><a href="https://www.linkedin.com/" target="_blank" class="fab fa-linkedin fa-2x" aria-hidden="true"></a></li>

      </ul>
    </div>
  </div>
</nav>