title: Change constraint second item
body: <p><a href="https://i.stack.imgur.com/yUbqW.png" rel="noreferrer"><img src="https://i.stack.imgur.com/yUbqW.png" alt="enter image description here"></a></p>
  
  <p>I have a view with this constraint. I want to animate it and move to bottom of <code>NavigationBar</code>. So i want to change <code>Second item</code> attribute to something like this:</p>
  
  <pre><code>UIView.animateWithDuration(15.5, delay: 0.0, options: UIViewAnimationOptions.CurveEaseInOut, animations: {
      if (self.isViewLoaded() &amp;&amp; self.view.window != nil) {
           //How to set bottom item ?
           self.storeSelectViewVerticalContainerConstraint.secondItem = self.navigationController?.view.bottom
           self.view.layoutIfNeeded()
      }
  }, completion: {(Bool) in})
  </code></pre>
  
  <p>This code returns error:</p>
  
  <blockquote>
    <p>Cannot assign to property: 'secondItem' is a get-only property</p>
  </blockquote>
  
  <p>Or if this method is impossible, how to calculate, and move object from middle to top of view with navigation bar.</p>