Fix compilation with Boost 1.65.0

Change-Id: Ib88b7e13bddb1728dd882c086e97edffdd696f0d
Refs: #4258
diff --git a/tests/core/logger.t.cpp b/tests/core/logger.t.cpp
index 11dcfa4..b2fb4c7 100644
--- a/tests/core/logger.t.cpp
+++ b/tests/core/logger.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2014-2016,  Regents of the University of California,
+/*
+ * Copyright (c) 2014-2017,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -30,6 +30,8 @@
 #include <boost/algorithm/string/classification.hpp>
 #include <boost/algorithm/string/split.hpp>
 
+#include <iostream>
+
 namespace nfd {
 namespace tests {