Security update to 11.1.2.

For more info see here:
https://about.gitlab.com/2018/07/26/security-release-gitlab-11-dot-1-dot-2-released/

Approved by: mentors (implicit)
MFH: 2018Q3
Security: 2da838f9-9168-11e8-8c75-d8cb8abf62dd