title: How to create dispatch queue in Swift 3
body: <p>In Swift 2, I was able to create queue with the following code:</p>
  
  <pre><code>let concurrentQueue = dispatch_queue_create("com.swift3.imageQueue", DISPATCH_QUEUE_CONCURRENT)
  </code></pre>
  
  <p>But this doesn't compile in Swift 3.  </p>
  
  <p>What is the preferred way to write this in Swift 3?</p>