Cleanup iostream includes

Change-Id: I16dd945998463975b140c7a010d64a112f95d8ba
diff --git a/tests/unit-tests/encoding/nfd-constants.t.cpp b/tests/unit-tests/encoding/nfd-constants.t.cpp
index c3fe54a..9a354fa 100644
--- a/tests/unit-tests/encoding/nfd-constants.t.cpp
+++ b/tests/unit-tests/encoding/nfd-constants.t.cpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
@@ -22,7 +22,9 @@
 #include "encoding/nfd-constants.hpp"
 
 #include "boost-test.hpp"
+
 #include <boost/lexical_cast.hpp>
+#include <sstream>
 
 namespace ndn {
 namespace nfd {