title: allowsBackForwardNavigationGestures = true not working in xcode 7.1
body: <pre><code>import UIKit
  import WebKit
  
  class ViewController: UIViewController, WKNavigationDelegate {
  
  var webView : WKWebView!
  
  override func loadView() {
      webView = WKWebView()
      webView.navigationDelegate = self
      self.view = webView
  }
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      let url = NSURL(string: "http://boooo.com")
      webView.loadRequest(NSURLRequest(URL: url!))
      webView.allowsBackForwardNavigationGestures = true
  
  
  
  }
  
  override func didReceiveMemoryWarning() {
      super.didReceiveMemoryWarning()
  
  }
  
  
  }
  </code></pre>
  
  <p>Everything works fine but allowsBackForwardNavigationGestures = true not working in xcode 7.1. can't go back and forward in wkwebview.</p>