To implement the flexbox utilities, follow this example...
https://www.example.com/code
<nav class="navbar navbar-fixed-top navbar-toggleable-sm navbar-inverse bg-inverse">
<div class="container d-flex flex-row flex-md-nowrap flex-wrap">
<a href="#" class="hidden-lg-up my-2 mr-3" data-toggle="collapse" data-target="#navbarCollapse" aria-controls="navbarCollapse" aria-expanded="false">
<i class="fa fa-bars text-white"></i>
</a>
<a class="navbar-brand" href="#">Brand</a>
<div class="navbar-collapse collapse flex-md-unordered flex-last" id="navbarCollapse">
<ul class="navbar-nav">
<li class="nav-item active">
<a class="nav-link" href="#">Link <span class="sr-only">Home</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Link</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Link</a>
</li>
</ul>
</div>
<div class="d-flex ml-auto">
<ul class="navbar-nav">
<li class="nav-item">
<a class="nav-link" href="#">Right</a>
</li>
</ul>
</div>
<div class="hidden-md-up w-100"><!--hidden spacer to force wrap--></div>
</div>
</nav>
https://www.example.com/code