NODE_CHROMIUM_DOWNLOAD_HOST behind authentication

[amar15code]

some organizations Nexus snapshots are behind authentication, need a way to set authentication for node_chromium_download_host, property, like _auth is set for npm registry like below

Nexus proxy registry pointing to http://registry.npmjs.org/
registry = https:///nexus/content/repositories/npmjs-registry/
; base64 encoded authentication token
_auth = <base 64 auth token>

[dtolstyi]

@amar15code If you could provide a PR I will check and merge it