tools: improve tooling around AUTHORS file

Replace tools/updateAuthors.awk with tools/update-authors.js. The new
tool generates an AUTHORS file that is stable-ordered alphanumerically.

Fixes #9077.

PR: #9088
PR-URL: https://github.com/joyent/node/pull/9088


Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>