Fix the `What's New?` phabricatorbot handler.

Summary: `What's new` has been broken for awhile, I've updated it to use the `feed.query` text view.

Test Plan: Start up a bot and say "What's new?"

Reviewers: epriestley, #blessed_reviewers

CC: fas, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8118