'start_period' for 'healthchecks' was added in Compose file version 3.4,
https://docs.docker.com/compose/compose-file/compose-versioning/#version-34
Bump docker-compose files' versions from 3.3 to 3.4
Without this, docker-compose (1.25 at least) returns
ERROR: The Compose file './contrib/docker-compose/caddy.yml' is invalid because:
services.db.healthcheck value Additional properties are not allowed ('start_period' was unexpected)