build: switch to C++17

Change-Id: Ie68020a04b7e20b74778b6d0370544ded55c5e26
diff --git a/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp b/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp
index c0d088a..c3682dd 100644
--- a/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp
+++ b/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2020,  Regents of the University of California,
+ * Copyright (c) 2014-2022,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -65,7 +65,7 @@
   BOOST_REQUIRE(m_keyChain.createIdentity("/A/B"));
   BOOST_REQUIRE(m_keyChain.createIdentity("/C/nrd"));
 
-  auto test = [this] (Name routeName, optional<ReadvertiseAction> expectedAction) {
+  auto test = [this] (Name routeName, std::optional<ReadvertiseAction> expectedAction) {
     auto policy = makePolicy();
     auto action = policy->handleNewRoute(makeNewRoute(routeName));
 
@@ -79,7 +79,7 @@
     }
   };
 
-  test("/D/app", nullopt);
+  test("/D/app", std::nullopt);
   test("/A/B/app", ReadvertiseAction{"/A", ndn::security::signingByIdentity("/A")});
   test("/C/nrd", ReadvertiseAction{"/C", ndn::security::signingByIdentity("/C/nrd")});
 }