Rename the `support/jshint` directory.

Summary: It is somewhat overkill to use an entire directory for a single file (the configuration file for JSHint). Instead, rename the directory so that it could (theoretically) be used for other linter configuration files.

Test Plan: Ran `arc lint -- webroot/rsrc/js/core/phtize.js` just to make sure everything still works.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9944