Merge branch 'russell/fix-service-desk-badge' into 'master'

Fix badge markup for the Service Desk page

See merge request gitlab-org/gitlab!31295

doc/user/project/service_desk.md

-# Service Desk **(Starter)**
+# Service Desk **(STARTER)**
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/149) in [GitLab Premium 9.1](https://about.gitlab.com/releases/2017/04/22/gitlab-9-1-released/#service-desk-eep).