Lets Encrypt certificate is not being installed

I'm running lua-resty-auto-ssl on the xenial OpenResty docker image using the standard installation instructions from the readme (LuaRocks, add the tasks to the config).

The issue I'm having is that the fallback cert is not being replaced by a Lets Encrypt cert, and I'm getting all sorts of self signed cert errors.

Some sort of communication with Lets Encrypt is clearly not occurring, but I'm not sure where the error is. I've looked at the `error.log` and there isn't an issue referring to letsencrypt there. Notably however, the file `letsencrypt/config` looks like its in a state prior to contacting Lets Encrypt because it contains the line `# This file will be overwritten by resty-auto-ssl.`.

Any help is appreciated! ✨

Start with the README installation instructions and reproduce the issue on the xenial OpenResty Docker image. Inspect error.log, letsencrypt/config, and the configured tasks to determine why communication with Let's Encrypt does not occur. Done means the fallback certificate is replaced by a Let's Encrypt certificate without self-signed certificate errors.

Written by the indexing model from the issue text.