Update title and revert section of 6.7-to-6.8 docs

doc/update/6.7-to-6.8.md

-# From 6.6 to 6.7
+# From 6.7 to 6.8
 
 ### 0. Backup
 
@@ -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
 
@@ -37,7 +39,7 @@ sudo -u git -H git checkout 6-8-stable-ee
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch
-sudo -u git -H git checkout v1.9.1
+sudo -u git -H git checkout v1.9.3
 ```
 
 ### 4. Install libs, migrations, etc.
@@ -114,10 +116,10 @@ To make sure you didn't miss anything run a more thorough check with:
 
 If all items are green, then congratulations upgrade is complete!
 
-## Things went south? Revert to previous version (6.6)
+## Things went south? Revert to previous version (6.7)
 
 ### 1. Revert the code to the previous version
-Follow the [`upgrade guide from 6.5 to 6.6`](6.5-to-6.6.md), except for the database migration 
+Follow the [`upgrade guide from 6.6 to 6.7`](6.6-to-6.7.md), except for the database migration 
 (The backup is already migrated to the previous version)
 
 ### 2. Restore from the backup: