title: UISplitViewController displayModeButtonItem not displaying
body: <p>I am not able to get iOS to display my button to show the <code>UISplitView</code> master view when in portrait mode (iPad) or landscape (iPhone 6+).</p>
  
  <p>Right now I am using the following code, but it's not doing anything...</p>
  
  <pre><code>    detailViewController.navigationItem.leftItemsSupplementBackButton = true
      detailViewController.navigationItem.leftBarButtonItem = displayModeButtonItem()
  </code></pre>
  
  <p>I tried putting that in the <code>viewDidLoad()</code> of my <code>UISplitView</code> subclass or in the <code>viewDidLoad()</code> of my detail main navigation controller.</p>
  
  <p>It does not seem to do anything so far... Am I missing something ?</p>