message: config: update FCOS Cincinnati endpoint (prod)
  This updates the default FCOS Cincinnati endpoint, switching from
  staging infrastructure to production one.
diff: -# Fedora CoreOS Cincinnati backend (staging service)
  +# Fedora CoreOS Cincinnati backend
  [cincinnati]
  -base_url= "https://updates.coreos.stg.fedoraproject.org"
  +base_url= "https://updates.coreos.fedoraproject.org"
  