Update Dehydrated to 0.7.1+ to fix issuance with Let's Encrypt

Let's Encrypt is enabling [asynchronous order finalization](https://community.letsencrypt.org/t/openresty-with-resty-auto-ssl-failing-with-curl-error-3/195924/8) which is [supported by Dehydrated](https://github.com/dehydrated-io/dehydrated/commit/58bd926e30eb3f298b65d0b96efb58cf81a5fd93), but only more recent versions.

Until Dehydrated is updated to 0.7.1 or later, AutoSSL will fail with an error like:
```
+ Requesting certificate...
err: ERROR: Problem connecting to server (post for ; curl returned with 3)
, context: ssl_certificate_by_lua*, client: X.Y.Z.11, server: 0.0.0.0:443
```

Start by locating where this project vendors or invokes Dehydrated, then inspect the current version reference. Update Dehydrated to 0.7.1 or later and verify the certificate issuance flow no longer produces the reported curl error when asynchronous order finalization is used.

Written by the indexing model from the issue text.