Cleanup iostream includes

Change-Id: I16dd945998463975b140c7a010d64a112f95d8ba
diff --git a/src/security/transform/stream-sink.cpp b/src/security/transform/stream-sink.cpp
index 58208c0..543e532 100644
--- a/src/security/transform/stream-sink.cpp
+++ b/src/security/transform/stream-sink.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2013-2016 Regents of the University of California.
+/*
+ * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -21,6 +21,8 @@
 
 #include "stream-sink.hpp"
 
+#include <ostream>
+
 namespace ndn {
 namespace security {
 namespace transform {