Bump gitlab-shell to 4.1.1

This fixes a compatibility issue with Git 2.11:

- Issue: gitlab-org/gitlab-ce#25301
- gitlab-shell MR: gitlab-org/gitlab-shell!112
- CE MR: gitlab-org/gitlab-ce!7967
- EE MR: gitlab-org/gitlab-ee!964

Signed-off-by: Rémy Coutable <remy@rymai.me>

GITLAB_SHELL_VERSION

-4.1.0
+4.1.1

doc/update/8.14-to-8.15.md

@@ -72,7 +72,7 @@ sudo -u git -H git checkout 8-15-stable-ee
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch --all --tags
-sudo -u git -H git checkout v4.1.0
+sudo -u git -H git checkout v4.1.1
 ```
 ### 6. Update gitlab-workhorse