build: switch to C++17

Change-Id: Ie68020a04b7e20b74778b6d0370544ded55c5e26
diff --git a/daemon/fw/access-strategy.hpp b/daemon/fw/access-strategy.hpp
index edcf63b..1aaa5ed 100644
--- a/daemon/fw/access-strategy.hpp
+++ b/daemon/fw/access-strategy.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2021,  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,
@@ -31,6 +31,8 @@
 
 #include <ndn-cxx/util/rtt-estimator.hpp>
 
+#include <unordered_map>
+
 namespace nfd {
 namespace fw {