kres_modules/prefill.lua:186: [prefill] configuration must be in table {owner name = {per-zone config}}

Hi,

I am getting this issue with:

prefill.config({['.'] = {url = 'https://www.internic.net/domain/root.zone', ca_file = '/etc/ssl/certs/ca-certificates.crt', interval = 86400}})

I have the following modules:

modules = {
  'policy',
  'view',
  'hints',
  'prefill',
  'serve_stale < cache',
  'workarounds < iterate',
  'stats',
  'predict'
}

But with the prefill.config, I get: 'kres_modules/prefill.lua:186: [prefill] configuration must be in table {owner name = {per-zone config}}'

And yet, it is the one provided in https://knot-resolver.readthedocs.io/en/stable/modules.html#cache-prefilling.