R1:d0e4e960419e

Lint the `webroot/rsrc/externals/javelin` directory

Summary: Fixes T6953. As discussed, this directory //should// be linted.

Test Plan: Ran `arc lint` on a file in `webroot/rsrc/externals/javelin` and saw linter errors.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6953

Differential Revision: https://secure.phabricator.com/D11375