title: Flatpickr onchange event set dateStr to -1 day
body: <p>I have 2 date pickers. Start Date and End Date. When the Start Date is selected I need the End Date to only allow the current selected Start Date minus one day.</p>
  <p>Start Date</p>
  <pre><code>var date1 = $('[data-toggle=&quot;startDate&quot;]').flatpickr(
    {
      enableTime: false,
      altInput: true,
      altFormat: &quot;F j, Y&quot;,
      dateFormat: &quot;Y-m-d&quot;,
      minDate: new Date().fp_incr(2),
      onChange: function(dateObj, dateStr) {
        date2.set('maxDate', dateStr)
      }
    }
  );
  </code></pre>
  <p>End Date</p>
  <pre><code>var date2 = $('[data-toggle=&quot;endDate&quot;]').flatpickr(
    {
       enableTime: true,
       altInput: true,
       altFormat: &quot;F j, Y h:i K&quot;,
       dateFormat: &quot;Y-m-d H:i&quot;,
    }
  );
  </code></pre>
  <p>On the Start Date how can I add <code>fp_incr(-1)</code> to the onChange: dateStr</p>