git-codereview: fix vet warning to fix build on Go 1.10

Change-Id: Ib4cee24d5b70f99dfbebf0aa05c85be6164ba835
Reviewed-on: https://go-review.googlesource.com/84216
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/git-codereview/util_test.go b/git-codereview/util_test.go
index 89753d3..133c93a 100644
--- a/git-codereview/util_test.go
+++ b/git-codereview/util_test.go
@@ -112,7 +112,7 @@
 	// but make sure the tests don't fail.
 	_, err := exec.LookPath("git")
 	if err != nil {
-		t.Skip("cannot find git in path: %v", err)
+		t.Skipf("cannot find git in path: %v", err)
 	}
 
 	tmpdir, err := ioutil.TempDir("", "git-codereview-test")