Always build in C++11 mode

refs: #1930

Change-Id: Iedad4a814e5c7e6a5486f2f7e16c45c356131792
diff --git a/src/route/face-map.hpp b/src/route/face-map.hpp
index 4bc2b68..ccd801b 100644
--- a/src/route/face-map.hpp
+++ b/src/route/face-map.hpp
@@ -24,6 +24,7 @@
 #define NLSR_FACE_MAP_HPP
 
 #include <ndn-cxx/common.hpp>
+#include <algorithm>
 
 namespace nlsr {