title: Moment js add month
body: <p>I got an error while trying to add month to a given date. I am not sure if it is an error or bug. Here is the code i'm trying. </p>
  
  <pre class="lang-js prettyprint-override"><code>    var date = moment('2019-06-22');
      var addMonth = moment(date).add(1,'M').calendar();
      //Output: 07/22/2019
  
      var date = moment('2019-06-23');
      var addMonth = moment(date).add(1,'M').calendar();
      //ouput: Last Tuesday at 12:00 AM
  </code></pre>