Update gitlab-shell to 2.5.3 in 7-8 update guide, fixes #8838

doc/update/7.7-to-7.8.md

@@ -37,7 +37,7 @@ sudo -u git -H git checkout 7-8-stable-ee
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch
-sudo -u git -H git checkout v2.4.3
+sudo -u git -H git checkout v2.5.3
 ```
 ### 4. Install libs, migrations, etc.
@@ -105,10 +105,10 @@ If all items are green, then congratulations upgrade is complete!
 If you are using GitHub as an OAuth provider for authentication, you should change the callback URL so that it 
 only contains a root URL (ex. `https://gitlab.example.com/`)
-## Things went south? Revert to previous version (7.6)
+## Things went south? Revert to previous version (7.7)
 ### 1. Revert the code to the previous version
-Follow the [upgrade guide from 7.5 to 7.6](7.5-to-7.6.md), except for the database migration
+Follow the [upgrade guide from 7.6 to 7.7](7.6-to-7.7.md), except for the database migration
 (The backup is already migrated to the previous version)
 ### 2. Restore from the backup: