title: date.getDate() is not a function. (In 'date.getDate()', 'date.getDate()' is undefined) FullCalendar in Ionic 3
body: <p>I'm coding on a Ionic 3 project where i use a FullCalendar plugin for display a calendar ui.
  I've a problem with this code in the module of page when i try to change background of a single day on calendar.
  I've used dayRender function of FullCalendar.</p>
  
  <pre><code>$('#calendar').fullCalendar({
  
              dayRender: function (date, cell) {
                var today = new Date('2017-09-11T00:40Z')
                if (date.getDate() == today.getDate()) {
                    this.cell.css("background-color", "red");
                }
              },
  });
  </code></pre>
  
  <p>I've this Runtime error in output:</p>
  
  <blockquote>
    <p>date.getDate() is not a function. (In 'date.getDate()',
    'date.getDate()' is undefined) FullCalendar in Ionic 3</p>
  </blockquote>
  
  <p>so i don't understand why, because date is a Date object that was already defined in FullCalendar library.</p>
  
  <p>Any Solutions?</p>
  
  <p>ps: Sorry for my bad english.</p>