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/8348
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>

.eslintrc

@@ -54,6 +54,7 @@ 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}]