title: UISwipeGesture not registering first swipe
body: <p>Here's my code in <code>viewDidLoad</code>: </p>
  
  <pre><code>//add a swipe gesture
  let downSwipe = UISwipeGestureRecognizer(target: self, action: #selector(rotateDial(_:)))
  downSwipe.direction = .down
  self.view.addGestureRecognizer(downSwipe)
  </code></pre>
  
  <p>The first time I swipe down it doesn't recognize the gesture. I read in another SO that the swipe gesture is registering itself on the first swipe. How do I fix that?</p>