net/http: deflake a test

I missed this one in codereview.appspot.com/70010050
Same thing, but different test.

Fixes windows-amd64-race and likely other Windows
machines failing like:
http://build.golang.org/log/0382bf0048bf5835a51a8a902df5c6fc73cd7ff5

LGTM=adg
R=rsc, adg
CC=golang-codereviews
https://golang.org/cl/71770043

src/pkg/net/http/client_test.go

@@ -599,8 +599,8 @@ func TestClientInsecureTransport(t *testing.T) {
 
 	select {
 	case v := <-errc:
-		if !strings.Contains(v, "bad certificate") {
-			t.Errorf("expected an error log message containing 'bad certificate'; got %q", v)
+		if !strings.Contains(v, "TLS handshake error") {
+			t.Errorf("expected an error log message containing 'TLS handshake error'; got %q", v)
 		}
 	case <-time.After(5 * time.Second):
 		t.Errorf("timeout waiting for logged error")