build: switch to C++17

Change-Id: Ie68020a04b7e20b74778b6d0370544ded55c5e26
diff --git a/daemon/mgmt/command-authenticator.hpp b/daemon/mgmt/command-authenticator.hpp
index 8d5158e..12c6c70 100644
--- a/daemon/mgmt/command-authenticator.hpp
+++ b/daemon/mgmt/command-authenticator.hpp
@@ -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,
@@ -31,6 +31,8 @@
 #include <ndn-cxx/mgmt/dispatcher.hpp>
 #include <ndn-cxx/security/validator.hpp>
 
+#include <unordered_map>
+
 namespace nfd {
 
 /** \brief Provides ControlCommand authorization according to NFD configuration file.