switch to go vendoring

vendor/github.com/grpc-ecosystem/go-grpc-middleware/makefile

@@ -0,0 +1,17 @@
+SHELL=/bin/bash
+
+GOFILES_NOVENDOR = $(shell go list ./... | grep -v /vendor/)
+
+all: vet fmt test
+
+fmt:
+	go fmt $(GOFILES_NOVENDOR)
+
+vet:
+	# do not check lostcancel, they are intentional.
+	go vet -lostcancel=false $(GOFILES_NOVENDOR)
+
+test: vet
+	./scripts/test_all.sh
+
+.PHONY: all test