blog: fix fmt format causing vet failures

Change-Id: I9f06963e12ca806d94bab94af209ab794cb32a36
Reviewed-on: https://go-review.googlesource.com/80141
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/blog/local_test.go b/blog/local_test.go
index b2a4419..a65d815 100644
--- a/blog/local_test.go
+++ b/blog/local_test.go
@@ -21,7 +21,7 @@
 	w := httptest.NewRecorder()
 	mux.ServeHTTP(w, r)
 	if w.Code != 200 {
-		t.Errorf("GET /: want code 200, got %d")
+		t.Errorf("GET /: code = %d; want 200", w.Code)
 	}
 	want := "The Go Programming Language Blog"
 	if !strings.Contains(w.Body.String(), want) {