Honour http proxy settings

I also installed under a university server which has a known proxy and just running wormhole send yields the same error. Why doesn't it pick up the proxy and send it through it? (it's both set on HTTP_PROXY and HTTPS_PROXY)

Originally posted by @ysig in https://github.com/magic-wormhole/magic-wormhole/issues/207#issuecomment-1708929383