golang：如何使用代理执行https请求

I am able to do a http or https client request without setting up a proxy,

enter code here
tr := &http.Transport{
    TLSClientConfig: &tls.Config{InsecureSkipVerify: true},     
}

client := &http.Client{}
client.Transport = tr

request, err := http.NewRequest("HEAD", "http://www.???.com", nil)
request.Header.Set("User-Agent", "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36")

resp, err := client.Do(request)

if err != nil {
    log.Fatalln(err)
    return
}
defer resp.Body.Close()

httpcode = resp.Status

This script is working ok, I get a 200 ok when I request https url, but if I set up proxy , the script:

proxyString := "https://47.91.179.xxx:443"
proxyUrl, _ := url.Parse(proxyString)

tr := &http.Transport{
    Proxy: http.ProxyURL(proxyUrl),
    TLSClientConfig: &tls.Config{InsecureSkipVerify: true}, 

}

client := &http.Client{}
client.Transport = tr

....................

I always get "Bad request", I read docs: https://golang.org/pkg/net/http/:

........... Starting with Go 1.6, the http package has transparent support for the HTTP/2 protocol when using HTTPS. Programs that must disable HTTP/2 can do so by setting Transport.TLSNextProto (for clients) or Server.TLSNextProto (for servers) to a non-nil, empty map. Alternatively, the following GODEBUG environment variables are currently supported: ..............

So, I tried to stop http2:

tr := &http.Transport{
    Proxy: http.ProxyURL(proxyUrl),
    //Proxy: http.ProxyFromEnvironment,
    TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
    TLSNextProto:    make(map[string]func(authority string, c *tls.Conn) http.RoundTripper),
}

same problem, "Bad request". I tried os.Setenv("HTTPS_PROXY", "47.91.???.???:443"), It is the same result. This is logged in server:

{S;}220.255.95.68{S;}-{S;}07/Mar/2017:17:01:47 +0800{S;}CONNECT www.panpacific.com:443 HTTP/1.1{S;}400{S;}173{S;}340{S;}-{S;}-{S;}-{S;}-{S;}-{S;}www.panpacific.com

So, Does golang support https client request via proxy? How do I get correct results?