build: suppress CryptoPP warnings

Change-Id: I52e93fb18c42cf72d73c4477dc4a8093a5221215
diff --git a/tests/security/test-signature-sha256.cpp b/tests/security/test-signature-sha256.cpp
index bb1b756..daf359b 100644
--- a/tests/security/test-signature-sha256.cpp
+++ b/tests/security/test-signature-sha256.cpp
@@ -9,9 +9,7 @@
 #include "security/key-chain.hpp"
 #include "security/validator.hpp"
 
-#include <cryptopp/base64.h>
-#include <cryptopp/hex.h>
-#include <cryptopp/files.h>
+#include "security/cryptopp.hpp"
 
 using namespace std;
 namespace ndn {