vendor: add cfssl dependency

vendor/github.com/cloudflare/cfssl/ocsp/config/config.go

@@ -0,0 +1,13 @@
+// Package config in the ocsp directory provides configuration data for an OCSP
+// signer.
+package config
+
+import "time"
+
+// Config contains configuration information required to set up an OCSP signer.
+type Config struct {
+	CACertFile        string
+	ResponderCertFile string
+	KeyFile           string
+	Interval          time.Duration
+}