core: unify version string

refs #2671

Change-Id: I88a58a500a43635cc8698c4bf444723d6e713590
diff --git a/core/common.hpp b/core/common.hpp
index 4085d68..e8afc87 100644
--- a/core/common.hpp
+++ b/core/common.hpp
@@ -57,6 +57,6 @@
 using boost::noncopyable;
 
 
-} // namespace
+} // namespace ndn
 
 #endif // NDN_TOOLS_CORE_COMMON_HPP