Bump cfssl to be compatible with Go 1.10

vendor/github.com/google/certificate-transparency-go/x509/root_plan9.go

@@ -0,0 +1,37 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build plan9
+
+package x509
+
+import (
+	"io/ioutil"
+	"os"
+)
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/sys/lib/tls/ca.pem",
+}
+
+func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
+	return nil, nil
+}
+
+func loadSystemRoots() (*CertPool, error) {
+	roots := NewCertPool()
+	var bestErr error
+	for _, file := range certFiles {
+		data, err := ioutil.ReadFile(file)
+		if err == nil {
+			roots.AppendCertsFromPEM(data)
+			return roots, nil
+		}
+		if bestErr == nil || (os.IsNotExist(bestErr) && !os.IsNotExist(err)) {
+			bestErr = err
+		}
+	}
+	return nil, bestErr
+}