deps: upgrade npm to 3.8.9

Contains the following three npm releases:
https://github.com/npm/npm/releases/tag/v3.8.7
https://github.com/npm/npm/releases/tag/v3.8.8
https://github.com/npm/npm/releases/tag/v3.8.9

PR-URL: https://github.com/nodejs/node/pull/6664


Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>