Fix CE install link for downgrade docs

doc/downgrade_ee_to_ce/README.md

@@ -70,7 +70,7 @@ To downgrade an Omnibus installation, it is sufficient to install the Community
 Edition package on top of the currently installed one. You can do this manually,
 by directly [downloading the package](https://packages.gitlab.com/gitlab/gitlab-ce)
 you need, or by adding our CE package repository and following the
-[CE installation instructions](https://about.gitlab.com/downloads/?version=ce).
+[CE installation instructions](https://about.gitlab.com/installation/?version=ce).
 
 **Source Installation**