Fix one human-readable timestamp, flag another

With cldr extension installed, Flow shows "Last modified about In 7
days" for posts that were actually modified "about 7 days ago". Flip the
$then and $now to match the getHumanTimestamp parameter.

Moderation is still wrong, e.g. "Deleted by Admin In 8 days".

Change-Id: Icea21aca370af47414cf688126af4d6c7ac49e2a
Merge "Fix one human-readable timestamp, flag another"