title: try..catch not catching async/await errors
body: <p>Perhaps I misunderstood how catching errors with <code>async/await</code> is supposed to work from things articles like this <a href="https://jakearchibald.com/2014/es7-async-functions/" rel="noreferrer">https://jakearchibald.com/2014/es7-async-functions/</a> and this <a href="http://pouchdb.com/2015/03/05/taming-the-async-beast-with-es7.html" rel="noreferrer">http://pouchdb.com/2015/03/05/taming-the-async-beast-with-es7.html</a>, but my <code>catch</code> block is not catching 400/500.</p>
  
  <pre><code>async () =&gt; {
    let response
    try {
     let response = await fetch('not-a-real-url')
    }
    catch (err) {
      // not jumping in here.
      console.log(err)
    }
  }()
  </code></pre>
  
  <p><a href="http://codepen.io/anon/pen/JYLwEW?editors=001" rel="noreferrer">example on codepen if it helps</a></p>