Fix ArcanistJSHintLinterTestCase::testLinter for recent JSHint
Recent JSHint improves the warning and attributes it to the equals sign
rather than the end of the expression (changed in 897e0359ce19, first
released in 2.11.0-rc1).
Test Plan: Ran arc unit with JSHint 2.12.0
Reviewers: epriestley, joshuaspence, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Differential Revision: https://secure.phabricator.com/D21503