title: Ambiguous use of 'sd_setImage(with:placeholderImage:completed:)' with Swift 3
body: <p>I am making the following call using <code>SDWebImage</code> on my <code>imageView</code>, which works fine with <code>Swift 2</code> but gives an error with <code>XCode 8 beta 5</code> compiling with <code>Swift 3</code>:</p>
  
  <pre><code> imageView.sd_setImage(with:url, placeholderImage:placeholder, completed: {
      (image: UIImage?, error: Error?, cacheType: SDImageCacheType, imageURL: URL?) in
              ...
      });
  </code></pre>
  
  <p>The error is:</p>
  
  <blockquote>
    <p>Ambiguous use of 'sd_setImage(with:placeholderImage:completed:)'</p>
  </blockquote>
  
  <p>I suspect I have something wrong in the signature for the completed handler, but I can't figure out what the syntax should be. What am I missing?</p>