go.crypto: Update for new crypto/x509 error.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5674046

ocsp/ocsp.go

@@ -153,7 +153,7 @@ func ParseResponse(bytes []byte) (*Response, error) {
 	}
 
 	if ret.Certificate.PublicKeyAlgorithm != x509.RSA || !basicResp.SignatureAlgorithm.Algorithm.Equal(idSHA1WithRSA) {
-		return nil, x509.UnsupportedAlgorithmError{}
+		return nil, x509.ErrUnsupportedAlgorithm
 	}
 
 	hashType := crypto.SHA1