title: items inside UIStackView overflowing
body: <p>I've created a <code>UIStackView</code> programmatically and inside placed <code>UITextView</code>s.<br>
  when the number of the <code>UITextView</code>s is more than 5 the boxes start overflowing off the screen. Here's a screenshot of the situation:</p>
  
  <p><a href="https://i.stack.imgur.com/cweP1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cweP1.png" alt="enter image description here"></a></p>
  
  <p>And here's the code : </p>
  
  <pre><code>let stackview = UIStackView(arrangedSubviews: letterBoxes)
  stackview.axis = .horizontal
  stackview.spacing = 10
  stackview.translatesAutoresizingMaskIntoConstraints = false
  self.view.addSubview(stackview)
  stackview.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
  stackview.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
  </code></pre>
  
  <p>what am I missing? 
  thank you </p>