mux.go
func methodNotAllowedHandler(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(405)
	w.Write(nil)
}
func methodNotAllowedHandler(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(405)
	w.Write(nil)
}
// methodNotAllowedHandler is a helper function to respond with a 405,
// method not allowed.