heroku pgbackups - Unknown command

This is a short one. If you try to access Heroku PGBackups with an old version of the gem, you'll get something like this...

$ heroku pgbackups
Unknown command. Run 'heroku help' for usage information.

If you run

$ heroku info

You won't see the pgbackups command in the list, either.

You just need to update the gem.
gem update heroku