title: Dictionary of type [NSObject: AnyObject] has no member "value(forKeyPath: ...)"
body: <p>I'm converting an app to swift3 and encountering the following problem.</p>
  
  <pre><code>@objc required init(response: HTTPURLResponse, representation: [NSObject : AnyObject])
  {
      if (representation.value(forKeyPath: "title") is String)    {
          self.title = **representation.value**(forKeyPath: "title") as! String
      }
  </code></pre>
  
  <p>I get the following error:</p>
  
  <blockquote>
    <p>Value of type [NSObject:AnyObject] has no member value.</p>
  </blockquote>
  
  <p>In the old version of the code I was just using AnyObject as type for representation, but if I do so I get the error <code>AnyObject is not a subtype of NSObject</code> there:</p>
  
  <pre><code>if (representation.value(forKeyPath: "foo") is String) {
      let elementObj = Element(response: response, representation:**representation.value(forKeyPath: "foo")**!)
  }
  </code></pre>