This also means that caddy source is fetched directly from upstream, as all
required fixes has been incorporated into the upstream.

Drop direct usage of gowork for now, in order to have caddy built using go
module, support for gowork with go modules might come later.

Follow new way of certificate managament in Caddy 1 as noted
https://github.com/mholt/caddy/issues/2588#issuecomment-505367152