Fix typo "in" to "is"

[pasabanov]

Fixed the typo "in" to "is" in the JavaScript / Appointment Time exercise.

[github-actions]

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[SleeplessByte]

Thanks. This will be up when the auto-deploy works again (it's temporarily off).

[SleeplessByte]

https://forum.exercism.org/t/fix-typo-in-to-is/17861/2