WebJars: Upgrade fullcalendar from 4.2.0 to 4.3.1 (Oct-2019)

As an admin, go to "Lessons" tool in a site. Click on "Add content" button. Click on "Embed calendar" link. If there is no events in calendar, then add some events in calendar tool. Get back to "Lessons" tool. This calendar is using fullcalendar library. Test it seeing its behaviour is the same as in Sakai 19.x. Also test: Create a recurring event in the calendar, have it repeat daily for 4 or 5 days Verify the event displays correctly when clicking on it in the calendar Click on Lessons -> Add Content -> Embed Calendar Click the event in the calendar Expected: the correct dates display, currently "invalid date" displays