net/http/httptest: fix incorrectly-named ResponseRecorder example

R=golang-dev, minux.ma, r
CC=golang-dev
https://golang.org/cl/8545047

src/pkg/net/http/httptest/example_test.go

@@ -12,7 +12,7 @@ import (
 	"net/http/httptest"
 )
 
-func ExampleRecorder() {
+func ExampleResponseRecorder() {
 	handler := func(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "something failed", http.StatusInternalServerError)
 	}