crypto/x509: use native compare in test instead of strings.Compare

Change-Id: I24c824edd8af6311a4eff44ef4bb28d73a91c68e
Reviewed-on: https://go-review.googlesource.com/41295Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/crypto/x509/verify_test.go

@@ -1415,7 +1415,7 @@ func TestUnknownAuthorityError(t *testing.T) {
 			hintCert: c,
 		}
 		actual := uae.Error()
-		if strings.Compare(actual, tt.expected) != 0 {
+		if actual != tt.expected {
 			t.Errorf("#%d: UnknownAuthorityError.Error() response invalid actual: %s expected: %s", i, actual, tt.expected)
 		}
 	}