title: iOS UITabBar : Remove top shadow gradient line
body: <p>I implemented a custom UITabBar and I still have this gradient/shadow on top of it. 
  I added</p>
  
  <p><code>[self.tabBar setBackgroundImage:[UIImage imageNamed:@"navBarBottom.png"]];</code> </p>
  
  <p>which is just changing the background but keeping the shadow gradient.</p>
  
  <p>What am I doing wrong ? Is there anything to specify to get rid of it ?</p>
  
  <p>What I have :</p>
  
  <p><img src="https://i.stack.imgur.com/pypqg.png" alt="top shadow"></p>
  
  <p>What I want : </p>
  
  <p><img src="https://i.stack.imgur.com/IxdxI.png" alt="without shadow"></p>
  
  <p>Thank you.</p>