use ndn::optional instead of boost::optional

Change-Id: If4db620ac410ddf5d8a082b26bdc8fef0b4c1b46
diff --git a/tests/unit-tests/configuration.t.cpp b/tests/unit-tests/configuration.t.cpp
index 7d5c901..e887165 100644
--- a/tests/unit-tests/configuration.t.cpp
+++ b/tests/unit-tests/configuration.t.cpp
@@ -45,7 +45,7 @@
   BOOST_CHECK_EQUAL(config.m_caItem.m_caPrefix, "/ndn");
   BOOST_CHECK_EQUAL(config.m_caItem.m_caInfo, "missing max validity period, max suffix length, and probe");
   BOOST_CHECK_EQUAL(config.m_caItem.m_maxValidityPeriod, time::seconds(86400));
-  BOOST_CHECK(!config.m_caItem.m_maxSuffixLength);
+  BOOST_CHECK(!config.m_caItem.m_maxSuffixLength.has_value());
   BOOST_CHECK_EQUAL(config.m_caItem.m_probeParameterKeys.size(), 0);
   BOOST_CHECK_EQUAL(config.m_caItem.m_supportedChallenges.size(), 2);
   BOOST_CHECK_EQUAL(config.m_caItem.m_supportedChallenges.front(), "pin");