message: MINOR: Fixes (updates slack link)
diff: ### [harp.gl site](https://www.harp.gl/)
  -### [harp.gl Slack channel](https://heredev.slack.com/messages/harpgl/) Registration available [here](https://join.slack.com/t/heredev/shared_invite/zt-km24s2k3-lYwF3L96ml51Ue_SBoUM3A).
  +### [harp.gl Slack channel](https://heredev.slack.com/messages/harpgl/) Registration available [here](https://join.slack.com/t/heredev/shared_invite/zt-nix6y5fb-WPQwpFlxZs1P4EJWhkrT9Q).
  ## Overview
  