title: use of unresolved identifier 'println' in swift 3
body: <p>I'm just a beginner with Swift. I am trying a very basic code, but unable to print things using 'println'.
  This is my code,</p>
  
  <pre><code>import Cocoa
  var myString:String? = nil
  if myString != nil {
      println(myString)
  }else {
      println("myString has nil value")
  }
  </code></pre>