Update docs for cert-manager

Since 5142bd73, we are using the official chart now.

doc/user/clusters/applications.md

@@ -82,10 +82,12 @@ certificates are valid and up-to-date.
 
 NOTE: **Note:**
 The
-[stable/cert-manager](https://github.com/helm/charts/tree/master/stable/cert-manager)
+[jetstack/cert-manager](https://github.com/jetstack/cert-manager)
 chart is used to install this application with a
 [`values.yaml`](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/vendor/cert_manager/values.yaml)
-file.
+file. Prior to GitLab 12.3, 
+the [stable/cert-manager](https://github.com/helm/charts/tree/master/stable/cert-manager)
+chart was used.
 
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