Add missing include

Change-Id: Ia23bdb82fed477859c0b18f6247a1c923c84951b
diff --git a/src/daemon/db-mgr.hpp b/src/daemon/db-mgr.hpp
index 9e79223..04b9672 100644
--- a/src/daemon/db-mgr.hpp
+++ b/src/daemon/db-mgr.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2017, Regents of the University of California.
+ * Copyright (c) 2014-2018, Regents of the University of California.
  *
  * This file is part of NDNS (Named Data Networking Domain Name Service).
  * See AUTHORS.md for complete list of NDNS authors and contributors.
@@ -24,6 +24,7 @@
 #include "zone.hpp"
 #include "rrset.hpp"
 
+#include <map>
 #include <ndn-cxx/common.hpp>
 #include <sqlite3.h>