tools: enforce JS brace style with linting

Enable `brace-style` in ESLint.

Ref: https://github.com/nodejs/node/pull/7094#discussion_r70149215
PR-URL: https://github.com/nodejs/node/pull/7630


Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>