Bump fullcalendar from 4.0.0-alpha.3 to 4.0.0-alpha.4

Bumps [fullcalendar](https://github.com/fullcalendar/fullcalendar) from 4.0.0-alpha.3 to 4.0.0-alpha.4.
- [Release notes](https://github.com/fullcalendar/fullcalendar/releases)
- [Changelog](https://github.com/fullcalendar/fullcalendar/blob/master/CHANGELOG.md)
- [Commits](https://github.com/fullcalendar/fullcalendar/compare/v4.0.0-alpha.3...v4.0.0-alpha.4

)

Signed-off-by: dependabot[bot] <support@dependabot.com>