deps,v8: fix compilation in VS2015

To compile with VS2015, the == and != methods in zone-allocator.h need
to be marked const.

This change was introduced upstream in
https://chromium.googlesource.com/v8/v8.git/+/f9e4527f32c2c268cb79428c74ea9703e9db3aec

PR-URL: https://github.com/nodejs/node/pull/2843


Reviewed-By: rvagg - Rod Vagg <rod@vagg.org>
Reviewed-By: orangemocha - Alexis Campailla <orangemocha@nodejs.org>
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>