title: overlapping date format in jquery
body: <p>I'm trying to set the datepicker up with a format like this </p>
  
  <pre><code>$("#date").datepicker({
  dateFormat: 'date_yyyy-mm-dd'
  });
  </code></pre>
  
  <p>I want it to output "date_2017-08-22"
  but the issue is that it outputs "22ate_20172017-08-22".
  Why is it doing that?</p>