build: remove --quiet from eslint invocation

All eslint rules are configured to report as errors. Remove useless
--quiet flag from eslint invocation in Makefile and vcbuild.bat.

PR-URL: https://github.com/nodejs/node/pull/5519


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>