Bump cfssl to 56268a6

vendor/github.com/cloudflare/cfssl/signer/signer.go

@@ -64,6 +64,12 @@ type SignRequest struct {
 	// for canonicalization) as the value of the notAfter field of the
 	// certificate.
 	NotAfter time.Time
+	// If ReturnPrecert is true a certificate with the CT poison extension
+	// will be returned from the Signer instead of attempting to retrieve
+	// SCTs and populate the tbsCert with them itself. This precert can then
+	// be passed to SignFromPrecert with the SCTs in order to create a
+	// valid certificate.
+	ReturnPrecert bool
 }
 
 // appendIf appends to a if s is not an empty string.