Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go tip
2. What operating system and processor architecture are you using (go env)?
   set GOARCH=amd64
   set GOBIN=
   set GOEXE=.exe
   set GOHOSTARCH=amd64
   set GOHOSTOS=windows
   set GOOS=windows
   set GOPATH=D:\gopath
   set GORACE=
   set GOROOT=D:\go
   set GOTOOLDIR=D:\go\pkg\tool\windows_amd64
   set CC=gcc
   set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\phuslu\AppData\Local\Temp\go-build318681378=/tmp/go-build -gno-record-gcc-switches
   set CXX=g++
   set CGO_ENABLED=1
3. What did you do?
   Write a google reverse proxy with x/net/http2, it convert request from http1 to http2 when browser visit google sites.
4. What did you expect to see?
   Browsers should works well with the reverse proxy.
5. What did you see instead?
   IE11 could not pass the proxy. the error is http2: invalid Connection request header
   Indeed, IE Sent Connection: Keep-Alive to the proxy and failed in checkConnHeaders