title: Glyphicon inside button not visible
body: <p>I would like to put glyphicon inside button. I don't know why it's not visible. The only thing that is visible is text, but not glyphicon.</p>
  
  <p><a href="http://codepen.io/FrenkyB/pen/mWGYJb?editors=1100" rel="nofollow noreferrer">Here</a> is example. Problem is with this button:</p>
  
  <pre><code>&lt;button type="button" class="btn btn-primary"&gt;
  &lt;span class="glyphicon glyphicon-arrow-up"&gt;&lt;/span&gt;3&lt;/button&gt;
  </code></pre>