src: update NODE_MODULE_VERSION to 94

Major V8 updates are usually API/ABI incompatible with previous
versions. This commit adapts NODE_MODULE_VERSION for V8 9.1.

Refs: https://github.com/nodejs/CTC/blob/master/meetings/2016-09-28.md

PR-URL: https://github.com/nodejs/node/pull/38273


Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Mary Marchini <oss@mmarchini.me>