title: SFSafariViewController crash: The specified URL has an unsupported scheme
body: <p>My code:</p>
  
  <pre><code>if let url = NSURL(string: "www.google.com") {
      let safariViewController = SFSafariViewController(URL: url)
      safariViewController.view.tintColor = UIColor.primaryOrangeColor()
      presentViewController(safariViewController, animated: true, completion: nil)
  }
  </code></pre>
  
  <p>This crashes on initialization only with exception:</p>
  
  <blockquote>
    <p>The specified URL has an unsupported scheme. Only HTTP and HTTPS URLs are supported</p>
  </blockquote>
  
  <p>When I use <code>url = NSURL(string: "http://www.google.com")</code>, everything is fine.
  I am actually loading URL's from API and hence, I can't be sure that they will be prefixed with <code>http(s)://</code>.</p>
  
  <p>How to tackle this problem? Should I check and prefix <code>http://</code> always, or there's a workaround?</p>