name+data: Small improvements

Change-Id: If366a2149cc52a6ee0e3113761772a6e9de6f735
diff --git a/include/ndn-cpp/data.hpp b/include/ndn-cpp/data.hpp
index e2d9451..6f0f397 100644
--- a/include/ndn-cpp/data.hpp
+++ b/include/ndn-cpp/data.hpp
@@ -15,6 +15,7 @@
 #include "signature.hpp"
 #include "meta-info.hpp"
 #include "key-locator.hpp"
+#include "security/signature/signature-sha256-with-rsa.hpp"
 
 namespace ndn {