In Calendar mobile month view, color circles green for attending events too

Summary: Ref T11816. We currently color circles green if you're invited, but should color them green if you're attending, too.

Test Plan: Viewed calendar mobile month view, saw attending events in green.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11816

Differential Revision: https://secure.phabricator.com/D16899