title: UIStackview not resizing when hiding the labels inside it
body: <p>Hi I'm new to UIStackViews.<br>
  So I have a vertical Stackview containing 8 Labels.<br>
  However, the problem with my Stackview is that whenever I hide the Labels inside it, my stackview does not resize.  </p>
  
  <p><a href="https://media.discordapp.net/attachments/422660792173985813/470431116029984779/Screen_Shot_2018-07-22_at_1.19.22_pm.png?width=267&amp;height=471" rel="nofollow noreferrer">The labels within the Red Rectangle are in my Stackview</a><br>
  <a href="https://media.discordapp.net/attachments/422660792173985813/470431168043679764/Screen_Shot_2018-07-22_at_1.19.09_pm_copy.png?width=274&amp;height=471" rel="nofollow noreferrer">When I hide those labels of the Stackview, I want my screen to look like this</a><br>
  <a href="https://media.discordapp.net/attachments/422660792173985813/470431265980416060/Screen_Shot_2018-07-22_at_1.19.09_pm.png?width=274&amp;height=471" rel="nofollow noreferrer">However for some reason when I hide those labels, it looks like this instead with all the space visible and the stuff at the bottom doesn't go up</a></p>
  
  <p>How do I fix this?<br>
  Here's how I hid the labels:  </p>
  
  <pre><code> override func viewDidLoad() {
          super.viewDidLoad()
          showingResultLabel.isHidden = true
          addressLabel.isHidden = true
          costOfKitLabel.isHidden = true
          costOfModularLabel.isHidden = true
          dispatchedFromLabel.isHidden = true
          kitHomecostLabel.isHidden = true
          modularHomecostLabel.isHidden = true
          dispatchFromLabel.isHidden = true
  </code></pre>
  
  <p>Thanks</p>