title: swift animateWithDuration not working in iOS 7
body: <p>I have an animation thats running fine in iOS 8.1 but in iOS 7.1 the button just appears where it is supposed to be without animation.</p>
  
  <p>The button has leading, trailing and bottom constraints of 0, and height constraint of 80. The constraints are setup in the storyboard.</p>
  
  <p>In the viewWillAppear method I change the bottom constraint to -80 so it isn't seen in the beginning.</p>
  
  <p>When the user presses a button, the button should animate up, I run this method:</p>
  
  <pre><code>func animateCtaUp() {
      self.ctaView.layoutIfNeeded()
      UIView.animateWithDuration(0.5, delay: 0, options: .CurveEaseOut, animations: {
              self.ctaViewBottomConstraint.constant = 0
              self.ctaView.layoutIfNeeded()
          }, completion: { finished in
  
      })
  }
  </code></pre>