Subject: [Acme] Correct error codes

From: Niklas Keller <[email-masked]>
Date: Sat, 27 Feb 2016 00:46:08 +0100

Hello,

today I noticed an inconsistency in the ACME spec, errors have two
different formats:

 * urn:acme:error:unauthorized
 * urn:acme:badNonce

I guess the one with `:error:` is the right one, but I'm not sure.

Can anyone clarify? I'd be happy to send a PR then.