util: Ensure ndn::RegexComponentMatcher works with Boost >= 1.56

Change-Id: I39c2c400317cf00a9a560e0b9d26f786ea5e3486
Refs: #1866
diff --git a/tests/unit-tests/util/test-regex.cpp b/tests/unit-tests/util/test-regex.cpp
index c5ef435..81630d1 100644
--- a/tests/unit-tests/util/test-regex.cpp
+++ b/tests/unit-tests/util/test-regex.cpp
@@ -59,6 +59,8 @@
   BOOST_CHECK_EQUAL(res, true);
   BOOST_CHECK_EQUAL(cm->getMatchResult().size(), 1);
   BOOST_CHECK_EQUAL(cm->getMatchResult()[0].toUri(), string("ccc.cd"));
+
+  BOOST_REQUIRE_EQUAL(backRef->size(), 2);
   BOOST_CHECK_EQUAL(backRef->getBackref(0)->getMatchResult()[0].toUri(), string("ccc"));
   BOOST_CHECK_EQUAL(backRef->getBackref(1)->getMatchResult()[0].toUri(), string("cd"));
 }