title: Shrink large title when scrolling (not UITableViewController) iOS 11
body: <p>I have got a View Controller embedded in a Navigation Controller with prefers large titles option set to true; inside the View Controller there’s a Scroll View.</p>
  <p>I want to make the nav bar shrink when scrolling.</p>
  <p>How could I achieve this?</p>
  <p><em>Xcode 9, Swift 4, iOS 11</em></p>