main/cvs: security upgrade to 1.12.12
Most distros uses 1.12.13 (https://repology.org/project/cvs/versions) but according to Gentoo it is usable, so following Gentoo (https://bugs.gentoo.org/124733) 1.12.12 is the way forward.
CVEs:
- CVE-2010-3846 - https://bugzilla.redhat.com/show_bug.cgi?id=642146
- CVE-2012-0804 - https://security-tracker.debian.org/tracker/CVE-2012-0804
- CVE-2017-12836 - https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=871810#10