Discovery: `plex_mediaserver` not valid?

Configuration
1

Using Hassio 0.80.0. I’m trying to enable discovery of Plex:

discovery:
  enable:
    - plex_mediaserver

But it’s failing saying plex_mediaserver is invalid:

Invalid config for [discovery]: value is not allowed @ data['discovery']['enable'][0]. Got 'plex_mediaserver'. (See /config/configuration.yaml, line 39). Please check the docs at https://home-assistant.io/components/discovery/

If you look at the discover page, it clearly states this is a valid option: https://home-assistant.io/components/discovery/

Did something update in 0.8 and not update in the docs?