Fix checkstyle severities
Summary: "Advice" is not a valid severity for Checkstyle... valid severities are ignore, info, warning and error.
Test Plan: Read the documentation.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D13684