title: add Shadow on UIView using swift 3
body: <p>prior swift 3 i was adding shadow in my UIView like this :</p>
  
  <pre><code>//toolbar is an UIToolbar (UIView)
  toolbar.layer.masksToBounds = false
  toolbar.layer.shadowOffset = CGSize(width: -1, height: 1)
  toolbar.layer.shadowRadius = 1
  toolbar.layer.shadowOpacity = 0.5
  </code></pre>
  
  <p>but the above code is not working in swift 3 , instead of shadow my whole View's color is turned to ugly gray</p>
  
  <p>anyone knows how can we add shadow in swift 3 ?</p>