encoding: make Block convertible to span

Change-Id: Idb501467d1c56b95e7fdb76acda63b919fe98f85
diff --git a/tools/ndnsec/cert-gen.cpp b/tools/ndnsec/cert-gen.cpp
index 51ad678..e44d063 100644
--- a/tools/ndnsec/cert-gen.cpp
+++ b/tools/ndnsec/cert-gen.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2021 Regents of the University of California.
+ * Copyright (c) 2013-2022 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -160,8 +160,7 @@
 
   {
     using namespace security::transform;
-    const auto& wire = cert.wireEncode();
-    bufferSource(make_span(wire.wire(), wire.size())) >> base64Encode(true) >> streamSink(std::cout);
+    bufferSource(cert.wireEncode()) >> base64Encode(true) >> streamSink(std::cout);
   }
 
   return 0;