honor HTTPS_PROXY environment variable

[finncolman]

This resolves issue 1064

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[finncolman]

See: ProxyFromEnvironment

The DefaultTransport looks like this:

var DefaultTransport RoundTripper = &Transport{
	Proxy: ProxyFromEnvironment,

This is what is missing from this custom transport

Also, this fork has been tested in my system so I know it fixes the proxy issue.

[milindl]

Hi @rayokota , asking for your review here, as you would know this much better than I.

Maybe the proxy can be specified via the configuration (as a function?), rather than only being set to being picked from the environment.

[rayokota]

Thanks for the PR @finncolman , LGTM