build: suppress CryptoPP warnings

Change-Id: I52e93fb18c42cf72d73c4477dc4a8093a5221215
diff --git a/src/util/io.hpp b/src/util/io.hpp
index 3d39feb..6026f06 100644
--- a/src/util/io.hpp
+++ b/src/util/io.hpp
@@ -13,9 +13,7 @@
 #include <string>
 #include <iostream>
 #include <fstream>
-#include <cryptopp/files.h>
-#include <cryptopp/base64.h>
-#include <cryptopp/hex.h>
+#include "../security/cryptopp.hpp"
 
 
 namespace ndn {