Update devel/rubygem-prometheus-client-mmap to 0.9.3 required for gitlab 10.8.x

[mfechner]

Summary

Commit message:
Update devel/rubygem-prometheus-client-mmap to 0.9.3 required for gitlab 10.8.x.

Test Plan

All patches are build, you can find all build logs:
https://pkg.fechner.net/jail.html?mastername=111amd64-gitlab

The fresh packages are tested against a new installation using:
https://gitlab.fechner.net/mfechner/Gitlab-vagrant

An old version is updated following the manual:
https://gitlab.fechner.net/mfechner/Gitlab-docu

[swills]

Approved