ServeHTTP does not use pointer.

Writing-a-Plugin:-HTTP-Middleware.md

@@ -36,7 +36,7 @@ type MyHandler struct {
 To implement the `httpserver.Handler` interface, we write a method called ServeHTTP. This method is the actual handler function, and, unless it fully handles the request by itself, it should call the next handler in the chain:
 
 ```go
-func (h *MyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
+func (h MyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 	return h.Next.ServeHTTP(w, r)
 }
 ```