build: switch to C++17

Change-Id: Id6217b5c993f3e4726e89773128b565e5f136bb6
diff --git a/tools/chunks/catchunks/main.cpp b/tools/chunks/catchunks/main.cpp
index 59ea8d8..e89d904 100644
--- a/tools/chunks/catchunks/main.cpp
+++ b/tools/chunks/catchunks/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2021, Regents of the University of California,
+ * Copyright (c) 2016-2022, Regents of the University of California,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University.
  *
@@ -45,8 +45,7 @@
 #include <boost/program_options/parsers.hpp>
 #include <boost/program_options/variables_map.hpp>
 
-namespace ndn {
-namespace chunks {
+namespace ndn::chunks {
 
 namespace po = boost::program_options;
 
@@ -309,8 +308,7 @@
   return 0;
 }
 
-} // namespace chunks
-} // namespace ndn
+} // namespace ndn::chunks
 
 int
 main(int argc, char* argv[])