doc: replace node-gyp link with nodejs/node-gyp

The node-gyp is now in the nodejs/node-gyp. This commit replaces the
repository owner link with the new nodejs/node-gyp link.

PR-URL: https://github.com/nodejs/node/pull/3320


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>