title: WKWebView evaluateJavaScript completionHandler not called in iOS 11
body: <pre><code>let eval = "getTarget('\(url.absoluteString)')"
  webView.evaluateJavaScript(eval, 
  completionHandler: {(response, error) in
  })
  </code></pre>
  
  <p>completionhandler does not get called in iOS 11 at all. Works fine on iOS 10.</p>
  
  <p>Anybody workaround for this? 
  OR
  Is there an alternative for evaluateJavaScript.</p>