title: NSNotification.Name.didBecomeActiveNotification not found
body: <p>I'm working on a macOS app on Xcode 10.1 with a 10.14 deployment target. According to the documentation there should be a NSNotification.Name.didBecomeActiveNotification, but the build fails with a <code>Type 'NSNotification.Name?' has no member 'didBecomeActiveNotification'</code> error. I have imported Cocoa, AppKit and Foundation. Here is the relevant code:</p>
  
  <pre><code>NotificationCenter.default.addObserver(forName: .didBecomeActiveNotification, object: nil, queue: nil) { notification in
      print("\(notification)")
  }
  </code></pre>
  
  <p>What is the problem?</p>