Commit 75f131da02c00027b9a8240fb74d117cb0f9d9cf added
`chown 'nginx:nginx' '/var/lib/acme'` to the pre-start script,
but since it doesn't use `chown -R`, it is possible that there
are older existing subdirs (like `acme-challenge`)
that are owned to `root` from before that commit went it.
ee0f3e7ad9