namespace: try to resolve ndn and std conflicts

Change-Id: I141ead4b8f30ce75bae73974e47e6e5acd75a296
diff --git a/src/main.cpp b/src/main.cpp
index 009f761..a1ed56c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -19,6 +19,7 @@
 INIT_LOGGER("MAIN");
 
 using namespace ndn;
+using ndn::shared_ptr;
 
 class NewApp : public QApplication
 {