tools: apply linting to custom rules code

Apply our eslint rules to the code for our custom eslint rules.

Eslint Inception! Maybe. I never saw that movie...

PR-URL: https://github.com/nodejs/node/pull/3195


Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Roman Reiss <me@silverwind.io>