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>

.eslintrc

@@ -55,6 +55,7 @@ rules:
 
   # Stylistic Issues
   # http://eslint.org/docs/rules/#stylistic-issues
+  brace-style: [2, "1tbs", {allowSingleLine: true}]
   comma-spacing: 2
   eol-last: 2
   indent: [2, 2, {SwitchCase: 1}]