Fix mail title in Countdown

Summary: Fixes T8959. Countdown now makes feed stories and emails.

Test Plan: Comment on, edit, a countdown.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8959

Differential Revision: https://secure.phabricator.com/D13738