R1:6507e846294b

Minor spacing update for Remarkup lists

Summary: Lists that have task objects look bad since the objects bleed into each other vertically. This provides slightly better spacing.

Test Plan: Review T9379 with new spacing.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14588