Fix Phriction link syntax a little more
Summary: This still wasn't quite right -- a link like [[ Porcupine Facts ]] with a space would not lookup correctly, and would render as porcupine_facts.
Test Plan: Verified that [[ Porcupine Facts ]] now works correctly.
Reviewers: chad
Reviewed By: chad
Differential Revision: https://secure.phabricator.com/D15780