title: Convert from Swift 3.x to 5
body: <p>When I opened my project in Xcode 10.2, I got this message:</p>
  
  <p>Unsupported Swift Version
  …Use Xcode 10.1 to migrate the code to Swift 4.</p>
  
  <p>Where can I still find Xcode 10.1? So the process is to have 2 versions of Xcode, first migrate to Swift 4 then 5?</p>
  
  <p>PS: If I migrate the code to Swift 5, does the app still bundle Swift binary? If yes, then what's the benefits since the app still bundle Swift binary? If no, then how does it handle iOS 11.x?</p>