ACMEv1 sunset at Let's Encrypt breaks `acme`

[darkk]

ACMEv1 sunset currently breaks at least acme reg:

$ acme reg -gen mailto:username@example.com
403 urn:acme:error:unauthorized: Account creation on ACMEv1 is disabled. Please upgrade your ACME client to a version that supports ACMEv2 / RFC 8555. See https://community.letsencrypt.org/t/end-of-life-plan-for-acmev1/88430 for details.

That's completely in-sync with the sunset plan outlined at the URL:

• November 2019 — stop new account registrations
• June 2020 — stop allowing new domains to validate
• June 2021 — entirely disable ACMEv1