title: Font awesome icons no longer working in "\f" content values
body: <p>I've recently upgraded to font awesome icons 5.1.0.
  But now the "\f" methods of putting icons into css content no longer works.</p>
  
  <p>For example:</p>
  
  <pre><code>.fc .fc-toolbar .fc-prev-button .ui-icon-circle-triangle-w:before {
      content: "\f00c";
  }
  </code></pre>
  
  <p>Is there a way around this?</p>