stop gitlab before backup

Stopping gitlab before backup ensures that backup has everything before upgrade incase something goes wrong. Also remove extra cd.

doc/update/7.3-to-7.4.md

 # From 7.3 to 7.4
 
-### 0. Backup
+### 0. Stop server
 
-```bash
-cd /home/git/gitlab
-sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
-```
+    sudo service gitlab stop
 
-### 1. Stop server
+### 1. Backup
 
 ```bash
-sudo service gitlab stop
-```
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
 
 ### 2. Get latest code
 
 ```bash
-cd /home/git/gitlab
 sudo -u git -H git fetch --all
 sudo -u git -H git checkout -- db/schema.rb # local changes will be restored automatically
 ```