util: add literal operators for duration types

Change-Id: I007fa61c80e535c6e4b12e85a32eeeee62fecc3c
Refs: #4468
diff --git a/src/mgmt/status-dataset-context.cpp b/src/mgmt/status-dataset-context.cpp
index dbf6774..2abbaa7 100644
--- a/src/mgmt/status-dataset-context.cpp
+++ b/src/mgmt/status-dataset-context.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) 2013-2018 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -24,7 +24,7 @@
 namespace ndn {
 namespace mgmt {
 
-const time::milliseconds DEFAULT_STATUS_DATASET_FRESHNESS_PERIOD = time::milliseconds(1000);
+const time::milliseconds DEFAULT_STATUS_DATASET_FRESHNESS_PERIOD = 1_s;
 
 const Name&
 StatusDatasetContext::getPrefix() const
@@ -113,7 +113,6 @@
   }
 
   m_state = State::FINALIZED;
-
   m_nackSender(resp);
 }