title: PFLoginViewController not showing Facebook login button with Swift
body: <p>Here is my Swift code:</p>
  
  <pre><code>        let loginViewController = PFLogInViewController()
          loginViewController.delegate = self;
          loginViewController.signUpController.delegate = self;
          loginViewController.fields = PFLogInFields.Facebook
          self.presentViewController(loginViewController, animated: animated, completion: nil)
  </code></pre>
  
  <p>I have tried everything possible, but don't know why it is not showing the Facebook login button. It just shows the default fields. </p>