Updated devel/gitaly to version 0.91.0

[mfechner]

Summary

Commit message:
Updated devel/gitaly to version 0.91.0 which is required for gitlab 10.6.x.

Reviewed by: tz/swills (mentor)
Approved by: tz/swills (mentor)
Differential Revision: URL to this revision

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]

LGTM