util: add literal operators for duration types

Change-Id: I007fa61c80e535c6e4b12e85a32eeeee62fecc3c
Refs: #4468
diff --git a/tests/unit-tests/security/v2/validation-policy-config.t.cpp b/tests/unit-tests/security/v2/validation-policy-config.t.cpp
index 7808700..31cba27 100644
--- a/tests/unit-tests/security/v2/validation-policy-config.t.cpp
+++ b/tests/unit-tests/security/v2/validation-policy-config.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2017 Regents of the University of California.
+ * Copyright (c) 2013-2018 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -232,7 +232,7 @@
   static time::milliseconds
   getRefreshTime()
   {
-    return time::hours(1);
+    return 1_h;
   }
 };
 
@@ -248,7 +248,7 @@
   static time::milliseconds
   getRefreshTime()
   {
-    return time::minutes(1);
+    return 1_min;
   }
 };
 
@@ -264,7 +264,7 @@
   static time::milliseconds
   getRefreshTime()
   {
-    return time::seconds(1);
+    return 1_s;
   }
 };