tools: enforce linting for unix-style line endings

PR-URL: https://github.com/nodejs/node/pull/6685


Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Ben Noorhduis <info@bnoordhuis.nl>