acme/autocert: remove trailing dot from domain before requesting cert

Browsers can send an SNI name of "example.com." for
https://example.com./ but LetsEncrypt rejects the trailing dot.

Fixes golang/go#18114

Change-Id: Ie38e355e5b5566a7eb18f77a2449660e22e21b4c
Reviewed-on: https://go-review.googlesource.com/33711
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2 files changed