Update docker-compose.yml

Fix reference for cron scheduling as crontab.guru uses a cron definition of 5 chars, which is not supported by watchtower written in go (requires 6 chron chars).

watchtower/docker-compose.yml

@@ -12,7 +12,7 @@ services:
       #- WATCHTOWER_NOTIFICATION_EMAIL_TO=john.doe@example.com
       #- WATCHTOWER_NOTIFICATION_EMAIL_SERVER=smtp.google.com
       #- WATCHTOWER_NOTIFICATIONS=email
-      - WATCHTOWER_SCHEDULE=0 0 6 * * * # see https://crontab.guru/
+      - WATCHTOWER_SCHEDULE=0 0 6 * * * # see https://containrrr.dev/watchtower/arguments/#scheduling
       - WATCHTOWER_CLEANUP=true # remove unused images afterwards
     image: containrrr/watchtower:latest
     labels: