net-mgmt/cacti: Update to 1.2.12

Changelog: https://github.com/Cacti/cacti/blob/release/1.2.12/CHANGELOG

PR: 246161
Submitted by: Michael Muenz <m.muenz@gmail.com> (maintainer)
MFH: 2020Q2
X-MFH-with: 531284
Security: cd864f1a-8e5a-11ea-b5b4-641c67a117d8