util: add literal operators for duration types

Change-Id: I007fa61c80e535c6e4b12e85a32eeeee62fecc3c
Refs: #4468
diff --git a/tests/unit-tests/util/notification-stream.t.cpp b/tests/unit-tests/util/notification-stream.t.cpp
index faedec8..3721091 100644
--- a/tests/unit-tests/util/notification-stream.t.cpp
+++ b/tests/unit-tests/util/notification-stream.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2014-2017 Regents of the University of California,
+/*
+ * Copyright (c) 2014-2018 Regents of the University of California,
  *                         Arizona Board of Regents,
  *                         Colorado State University,
  *                         University Pierre & Marie Curie, Sorbonne University,
@@ -26,10 +26,10 @@
  */
 
 #include "util/notification-stream.hpp"
-#include "simple-notification.hpp"
 #include "util/dummy-client-face.hpp"
 
 #include "boost-test.hpp"
+#include "simple-notification.hpp"
 #include "../identity-management-time-fixture.hpp"
 
 namespace ndn {
@@ -48,11 +48,10 @@
   SimpleNotification event1("msg1");
   notificationStream.postNotification(event1);
 
-  advanceClocks(time::milliseconds(1));
+  advanceClocks(1_ms);
 
   BOOST_REQUIRE_EQUAL(face.sentData.size(), 1);
-  BOOST_CHECK_EQUAL(face.sentData[0].getName(),
-                    "/localhost/nfd/NotificationStreamTest/%FE%00");
+  BOOST_CHECK_EQUAL(face.sentData[0].getName(), "/localhost/nfd/NotificationStreamTest/%FE%00");
   SimpleNotification decoded1;
   BOOST_CHECK_NO_THROW(decoded1.wireDecode(face.sentData[0].getContent().blockFromValue()));
   BOOST_CHECK_EQUAL(decoded1.getMessage(), "msg1");
@@ -60,11 +59,10 @@
   SimpleNotification event2("msg2");
   notificationStream.postNotification(event2);
 
-  advanceClocks(time::milliseconds(1));
+  advanceClocks(1_ms);
 
   BOOST_REQUIRE_EQUAL(face.sentData.size(), 2);
-  BOOST_CHECK_EQUAL(face.sentData[1].getName(),
-                    "/localhost/nfd/NotificationStreamTest/%FE%01");
+  BOOST_CHECK_EQUAL(face.sentData[1].getName(), "/localhost/nfd/NotificationStreamTest/%FE%01");
   SimpleNotification decoded2;
   BOOST_CHECK_NO_THROW(decoded2.wireDecode(face.sentData[1].getContent().blockFromValue()));
   BOOST_CHECK_EQUAL(decoded2.getMessage(), "msg2");