title: Fullcalendar.io - wrong date range highlighted from json
body: <p>I am having a problem displaying events in my calendar. I'm taking data from an events.json file and adding an event. It displays one day too short for me. For example, the event 09.08-15.08 is displayed only until 14.08.
  08.09-09.10 is correct,
  24.09-26.09 is too short
  01.09-05.09 is too short etc.</p>
  <p>Why is this happening? And how to fix it?</p>
  <p>Here is live preview of problem: <a href="https://mawk.bieda.it/" rel="nofollow noreferrer">https://mawk.bieda.it/</a></p>
  <p>Here is my code:</p>
  <pre><code>&lt;script&gt;
      document.addEventListener('DOMContentLoaded', function () {
  
          var calendarEl = document.getElementById('calendar');
  
          var calendar = new FullCalendar.Calendar(calendarEl, {
  
              /*locale: 'pl',*/
              firstDay: 1,
              headerToolbar: {
                  left: 'prev,next today',
                  center: 'title',
                  right: 'prevYear,nextYear'
              },
              validRange: {
                  start: '2021-01-01',
                  end: '2022-01-01'
              },
              selectable: true,
              select: function (info) {
                  alert('Selected ' + info.startStr + ' to ' + info.endStr);
              },
              events: {
                  url: '/events.json',
                  extraParams: function () {
                      return {
                          cachebuster: new Date().valueOf()
                      };
                  }
              },
  
          });
  
          calendar.render();
      });
  &lt;/script&gt;
  
  &lt;div id='calendar' style=&quot;height: 600px; width: 600px; margin: auto;&quot;&gt;&lt;/div&gt;
  </code></pre>
  <p>This is event.json:</p>
  <pre><code>[
      {
      &quot;title&quot;: &quot;09.08-15.08&quot;,
      &quot;start&quot;: &quot;2021-08-09&quot;,
      &quot;end&quot;: &quot;2021-08-15&quot;
      },
      {
      &quot;title&quot;: &quot;08.09-09.10&quot;,
      &quot;start&quot;: &quot;2021-09-08&quot;,
      &quot;end&quot;: &quot;2021-09-10&quot;
      },
      {
      &quot;title&quot;: &quot;24.09-26.09&quot;,
      &quot;start&quot;: &quot;2021-09-24&quot;,
      &quot;end&quot;: &quot;2021-09-26&quot;
      },
      {
      &quot;title&quot;: &quot;01.09-05.09&quot;,
      &quot;start&quot;: &quot;2021-09-01&quot;,
      &quot;end&quot;: &quot;2021-09-05&quot;
      },
      {
      &quot;title&quot;: &quot;28.09-03.10&quot;,
      &quot;start&quot;: &quot;2021-09-28&quot;,
      &quot;end&quot;: &quot;2021-10-03&quot;
      },
      {
      &quot;title&quot;: &quot;01.12-03.10&quot;,
      &quot;start&quot;: &quot;2021-12-01&quot;,
      &quot;end&quot;: &quot;2021-12-31&quot;
      }
      ]
  </code></pre>