Update calendar.md

2 jobs for master in 15 seconds (queued for 1 second)
Name Stage Failure
failed
build Build
ERROR 2020/03/31 00:47:56 [de] REF_NOT_FOUND: Ref "/de/calendar/" from page "services/calendar.md": page not found
ERROR 2020/03/31 00:47:56 [de] REF_NOT_FOUND: Ref "/services/help/" from page "services/calendar.md": page not found
ERROR 2020/03/31 00:47:56 [de] REF_NOT_FOUND: Ref "/de" from page "services/calendar.md": page not found
ERROR 2020/03/31 00:47:56 [de] REF_NOT_FOUND: Ref "/de/calendar/" from page "services/calendar.md": page not found
Total in 279 ms
Error: Error building site: logged 9 error(s)
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1