Avoid deprecated ndn-cxx functions

Change-Id: I763368c2ea12902b4ea400f92c23b17ad5a5628e
diff --git a/tests/identity-management-fixture.cpp b/tests/identity-management-fixture.cpp
index 4e6f731..b13c44a 100644
--- a/tests/identity-management-fixture.cpp
+++ b/tests/identity-management-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,
@@ -128,7 +128,7 @@
   certificate.setFreshnessPeriod(time::hours(1));
 
   // set content
-  certificate.setContent(key.getPublicKey().data(), key.getPublicKey().size());
+  certificate.setContent(key.getPublicKey());
 
   // set signature-info
   ndn::SignatureInfo info;