core: move event-emitter to core

Change-Id: I76f6fc7d8c4731bbbb95ea257e339e15b96dbea1
diff --git a/daemon/face/face.hpp b/daemon/face/face.hpp
index d6da710..9ff2d20 100644
--- a/daemon/face/face.hpp
+++ b/daemon/face/face.hpp
@@ -8,7 +8,7 @@
 #define NFD_FACE_FACE_H
 
 #include "common.hpp"
-#include "util/event-emitter.hpp"
+#include "core/event-emitter.hpp"
 
 namespace nfd {