Unify markdown syntax for Bash commands

doc/update/6.3-to-6.4.md

@@ -9,7 +9,9 @@ sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
 
 ### 1. Stop server
 
-    sudo service gitlab stop
+```bash
+sudo service gitlab stop
+````
 
 ### 2. Get latest code
 
@@ -51,18 +53,24 @@ sudo cp lib/support/init.d/gitlab /etc/init.d/gitlab
 
 ### 5. Start application
 
-    sudo service gitlab start
-    sudo service nginx restart
+```bash
+sudo service gitlab start
+sudo service nginx restart
+```
 
 ### 6. Check application status
 
 Check if GitLab and its environment are configured correctly:
 
-    sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production
+```bash
+sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production
+```
 
 To make sure you didn't miss anything run a more thorough check with:
 
-    sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
+```bash
+sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
+```
 
 If all items are green, then congratulations upgrade complete!