build: require gcc >= 5.3 and switch to C++14

Change-Id: I93c8fc238cc2654346bbc69a9d8ea83d1c0b099e
Refs: #3076, #4462
diff --git a/src/communication/sync-logic-handler.cpp b/src/communication/sync-logic-handler.cpp
index 7703505..308a15d 100644
--- a/src/communication/sync-logic-handler.cpp
+++ b/src/communication/sync-logic-handler.cpp
@@ -45,7 +45,7 @@
 
 SyncLogicHandler::SyncLogicHandler(ndn::Face& face, const IsLsaNew& isLsaNew,
                                    const ConfParameter& conf)
-  : onNewLsa(ndn::make_unique<OnNewLsa>())
+  : onNewLsa(std::make_unique<OnNewLsa>())
   , m_syncFace(face)
   , m_isLsaNew(isLsaNew)
   , m_confParam(conf)