On a server which has IPv6 configured, `sudo certbot --nginx` would fail because certbot looks for both A and AAAA DNS records, and if AAAA (IPv6) is found it uses that.
By adding:
```
listen 80;
listen [::]:80;
```
issue #22 is solved. Servers which have only IPv4 configured will continue working normally.
Based on caddy-gen
This will start a reverse proxy on port 80 and 443, which proxies
to the plausible container. Note that it will clash with any
existing reverse proxies on the host machine
