Fix issue 4785 - missing gitlab-shell part in update guide

doc/update/5.3-to-5.4.md

@@ -17,9 +17,14 @@ sudo -u git -H RAILS_ENV=production bundle exec rake gitlab:backup:create
 ### 2. Get latest code
 ```bash
+# GitLab
 cd /home/git/gitlab
 sudo -u git -H git fetch
 sudo -u git -H git checkout 5-4-stable
+# GitLab Shell
+cd /home/git/gitlab-shell
+sudo -u git -H git fetch
+sudo -u git -H git checkout v1.5.0
 ```
 ### 3. Install libs, migrations, etc.