title: use promise series instead async series
body: <p>I use the following async.js code </p>
  
  <pre><code>var arr = ['1', '2'];
  async.mapSeries(arr, getInfo, (e, res) =&gt; {
    console.log(res);
  });
  
  function getInfo(name, callback) {
    setTimeout(() =&gt; {
      callback(null, name + ' from async');
    }, 500);
  }
  </code></pre>
  
  <p>Now I want to convert it to bluebird <a href="http://bluebirdjs.com/docs/api/promise.mapseries.html" rel="nofollow">promise</a> and I try the following but the delay is not working, I think that probably I need to and the Promise.delay but not sure how to use it...</p>
  
  <pre><code>Promise.mapSeries(arr, function(getInfo) {
    return getInfo + ' from promise'
  }).then(function(results) {
    console.log(results)
  });
  </code></pre>