Use Boost.Operators in more places

Change-Id: I7024c3e7d4c30c99ec7a895d484f227cb60fb356
diff --git a/tests/unit/security/pib/key.t.cpp b/tests/unit/security/pib/key.t.cpp
index 5273436..a3c1806 100644
--- a/tests/unit/security/pib/key.t.cpp
+++ b/tests/unit/security/pib/key.t.cpp
@@ -29,6 +29,8 @@
 
 using namespace ndn::security::pib;
 
+BOOST_CONCEPT_ASSERT((boost::EqualityComparable<Key>));
+
 BOOST_AUTO_TEST_SUITE(Security)
 BOOST_FIXTURE_TEST_SUITE(TestKey, PibDataFixture)