Security update to 11.6.1.
For more details see here:
https://about.gitlab.com/2018/12/31/security-release-gitlab-11-dot-6-dot-1-released/

Approved by: mentors (implicit)
MFH: 2019Q1
Security: b2f4ab91-0e6b-11e9-8700-001b217b3468