tools: lint for alignment of variable assignments

Enforce alignment/indentation on variable assignments that span multiple
lines.

PR-URL: https://github.com/nodejs/node/pull/6242


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>