title: moment.js / date Appearing as NaN on iOS
body: <p>I'm getting <code>NaN</code> on calculation of date in iOS. For desktop and Android, it works perfectly, but iOS and Safari, I get <code>NaN</code></p>
  
  <p>Here's my code:</p>
  
  <p><code>last_visit_date</code> is coming from the database, it comes ex: <code>"2019-06-07T00:00:00.000Z"</code></p>
  
  <pre><code>let formattedLastVisitDate = moment(last_visit_date).format('MM-DD-YYYY') --- RESULT: "06-06-2019"
  
  let testing = moment(formattedLastVisitDate).add('30', 'days').format('MM-DD-YYYY') -- RESULT "Invalid Date"
  
  let add14Days = moment(testing).add('14', 'days').format('MM-DD-YYYY') -- RESULT "Invalid Date"
  </code></pre>
  
  <p>Why is this logic failing just on iOS?</p>