Update 7.7-to-7.8.md

doc/update/7.7-to-7.8.md

@@ -70,7 +70,7 @@ sudo cp lib/support/init.d/gitlab /etc/init.d/gitlab
 There are new configuration options available for [`gitlab.yml`](config/gitlab.yml.example). View them with the command below and apply them to your current `gitlab.yml`.
 
 ```
-git diff origin/7-6-stable:config/gitlab.yml.example origin/7-8-stable:config/gitlab.yml.example
+git diff origin/7-7-stable:config/gitlab.yml.example origin/7-8-stable:config/gitlab.yml.example
 ```
 
 #### Change Nginx settings