title: UIBarButtonItem appearance setBackgroundImage black line under buttons
body: <p>I have a little black line under all of my buttons which are in <code>UIControlStateNormal</code>. Back buttons and Done buttons are not affected.</p>
  
  <p>Here is image:</p>
  
  <p><img src="https://i.stack.imgur.com/HFH1s.png" alt="enter image description here"></p>
  
  <p>You can clearly see it, and it's super annoying. Here is how I'm setting all of my images:</p>
  
  <pre><code>[[UIBarButtonItem appearance] setBackgroundImage:[UIImage imageNamed:@"nav-button"] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
  </code></pre>
  
  <p>I'm using the same technique for back and done buttons, which doesn't have issues.</p>