x/crypto/ocsp: correct OID for DSA-with-SHA-256.

This was incorrect in crypto/x509 and go copied here.
See https://go-review.googlesource.com/#/c/20549 for the fix to
crypto/x509.

Fixes golang/go#14663.

Change-Id: I1fdca4b3f3edfeef1ee4ae01b1cf252ad8471163
Reviewed-on: https://go-review.googlesource.com/20550
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

ocsp/ocsp.go

@@ -144,7 +144,7 @@ var (
 	oidSignatureSHA384WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 12}
 	oidSignatureSHA512WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 13}
 	oidSignatureDSAWithSHA1     = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 3}
-	oidSignatureDSAWithSHA256   = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 4, 3, 2}
+	oidSignatureDSAWithSHA256   = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 3, 2}
 	oidSignatureECDSAWithSHA1   = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 1}
 	oidSignatureECDSAWithSHA256 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 2}
 	oidSignatureECDSAWithSHA384 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 3}