added getLinterConfigurationName() to ArcanistJSHintLinter.

Summary: Needed for it to be usable from ArcanistConfigurationDrivenLintEngine, which is pretty ok.

Test Plan: put jshint in your .arclint and feel the electricity in the air.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D7200