title: SDWebImage changing images while tableview scrolling
body: <p>There is a TableView with Cells and there is ImageView in each of them.
  I use SDWebImage to load images and it works fine, but when I scroll fast - I see that images in cells are changing few times before it will be right image.</p>
  
  <p>Why is it happening? What should I do?</p>
  
  <p>p.s. I tried use it with  or without placeholder with same result</p>
  
  <pre><code>imageView.sd_setImage(with: URL(string : myImageURL), placeholderImage: UIImage(named: "default.jpg"))
  </code></pre>