tools: update ESLint to 5.6.1

Update ESLint to 5.6.1.

PR-URL: https://github.com/nodejs/node/pull/23149


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>