util: add literal operators for duration types

Change-Id: I007fa61c80e535c6e4b12e85a32eeeee62fecc3c
Refs: #4468
diff --git a/tests/unit-tests/security/v2/validator-fixture.hpp b/tests/unit-tests/security/v2/validator-fixture.hpp
index 7f52048..c9a5763 100644
--- a/tests/unit-tests/security/v2/validator-fixture.hpp
+++ b/tests/unit-tests/security/v2/validator-fixture.hpp
@@ -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).
  *
@@ -43,7 +43,7 @@
     : face(io, {true, true})
     , validator(make_unique<ValidationPolicy>(), make_unique<CertificateFetcher>(face))
     , policy(static_cast<ValidationPolicy&>(validator.getPolicy()))
-    , cache(time::days(100))
+    , cache(100_days)
   {
     processInterest = [this] (const Interest& interest) {
       auto cert = cache.find(interest);