title: pushViewController not working in swift 3
body: <p>I am using storyboard and xib in swift 3 (iOS 10 and XCode 8). And when i load any View Controller with xib, application is crashing.</p>
  
  <p>Here is the code, i am using to load View Controller on Button Action:</p>
  
  <pre><code>let serverViewController = ServerViewController(nibName: "ServerViewController", bundle: nil)
  self.navigationController?.pushViewController(serverViewController, animated: true)
  </code></pre>