www/gitlab: fix regression from 40d54199a8b5b902f127d6f3db01ecc250586dc3

Relaxe redis dependency, regarding the redis changelog, there is no
breaking change in the new version.
As the redis gem is also used by rails it does not make sense to
duplicate the complete rails ports for gitlab.

(cherry picked from commit 9630bdc16b3e7f9c75cb18c2bf42457a8cea5655)