Convert to span and avoid deprecated ndn-cxx functions

Change-Id: I45c50527fe53498b53a3d951458bdff8e7d7778c
diff --git a/tests/key-chain-fixture.cpp b/tests/key-chain-fixture.cpp
index c71f175..faca165 100644
--- a/tests/key-chain-fixture.cpp
+++ b/tests/key-chain-fixture.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2020,  Regents of the University of California,
+ * Copyright (c) 2014-2022,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -60,7 +60,7 @@
   cert.setFreshnessPeriod(1_h);
 
   // set content
-  cert.setContent(key.getPublicKey().data(), key.getPublicKey().size());
+  cert.setContent(key.getPublicKey());
 
   // set signature info
   ndn::SignatureInfo info;