rib+tools: subscribe to FaceMonitor notifications using connect

refs #2350

Change-Id: I1b1b33cdcc3638c7344b6c690f928aff25aa5c8c
diff --git a/rib/rib-manager.cpp b/rib/rib-manager.cpp
index ae64820..e577626 100644
--- a/rib/rib-manager.cpp
+++ b/rib/rib-manager.cpp
@@ -126,7 +126,7 @@
   }
 
   NFD_LOG_INFO("Start monitoring face create/destroy events");
-  m_faceMonitor.onNotification += bind(&RibManager::onNotification, this, _1);
+  m_faceMonitor.onNotification.connect(bind(&RibManager::onNotification, this, _1));
   m_faceMonitor.start();
 
   scheduleActiveFaceFetch(ACTIVE_FACE_FETCH_INTERVAL);