The dashboard requires Plex Web v3.81.1 — that version is currently only available in the hosted version of Plex Web (https://app.plex.tv/desktop)
From the related blog entry:
You’ll need the latest version of the Plex Media Server (v1.14.1 or newer) and our web app (v3.81.1 or newer; available now in our hosted web app and coming to the bundled server version soon) to see all this deliciousness.
From the Plex Media Server release notes for v1.14.1 (public):
