tris: update Go to 1.9

Use Go 1.9 (go1.9) with a patch to enable users to access the 0RTT API:

    net/http: attach TLSConnContextKey to the request Context

README.md

@@ -23,7 +23,7 @@ So, to build with tls-tris, you need to use a custom GOROOT.
 A script is provided that will take care of it for you: `./_dev/go.sh`.
 Just use that instead of the `go` tool.
 
-The script also transparently fetches the custom Cloudflare Go 1.8rc3 compiler with the required backports.
+The script also transparently fetches the custom Cloudflare Go 1.9 compiler with the required backports.
 
 ```
 ./_dev/go.sh build ./_dev/tris-localserver

_dev/Makefile

@@ -22,15 +22,15 @@ endif
 
 # Note: when changing this, if it doesn't change the Go version
 # (it should), you need to run make clean.
-GO_COMMIT := 98882e950cbb48ce7aad4b5b9972601d3438fbe5
+GO_COMMIT := 88253a956a753213617d95af3f42a23a78798473
 
 .PHONY: go
 go: go/.ok_$(GO_COMMIT)_$(GOENV)
 
 go/.ok_$(GO_COMMIT)_$(GOENV):
 	rm -rf go/.ok_*_$(GOENV) go/$(GOENV)
 	mkdir -p go
-	git clone --branch 1.8 --single-branch --depth 25 https://github.com/cloudflare/go go/$(GOENV)
+	git clone --branch 1.9 --single-branch --depth 25 https://github.com/cloudflare/go go/$(GOENV)
 	cd go/$(GOENV) && git checkout $(GO_COMMIT)
 	cd go/$(GOENV)/src && GOROOT_BOOTSTRAP="$(shell $(GO) env GOROOT)" ./make.bash
 	@touch "$@"