Bump calendar-js from `fc37c33` to `6efebf4`

Bumps [calendar-js](https://github.com/georgehrke/calendar-js) from `fc37c33` to `6efebf4`.
- [Release notes](https://github.com/georgehrke/calendar-js/releases)
- [Commits](https://github.com/georgehrke/calendar-js/compare/fc37c335684f6f76c6869aa9ef661d8aba42ded4...6efebf4f1fe280d4dd4da088ac1515d919e41a19

)

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