Support HTTPS_PROXY

[winstliu]

• Node Version: 10.15.3, 6.9.0
• Platform: Windows Enterprise 10.0.18362 N/D Compilación 18362
• Compiler: N/A
• Module: N/A

node-gyp supports basic proxy options:

node-gyp/lib/install.js

Lines 432 to 435 in 721eb69

	var proxyUrl = gyp.opts.proxy
	|| env.http_proxy
	|| env.HTTP_PROXY
	|| env.npm_config_proxy

However, it doesn't look like it supports HTTPS_PROXY (and variants).
Would this be something that node-gyp is willing to support? I can create a PR if the answer is yes.

[bzoz]

Sure, PRs are always welcomed!

[rvagg]

closing in favour of PR @ #1751