util: generate random bytes using OpenSSL instead of CryptoPP

Change-Id: I68bdac565242432fa53a1f113d6f395bf3c6e982
Refs: #3010, #2949
diff --git a/src/security/detail/openssl.hpp b/src/security/detail/openssl.hpp
index 09a6f68..d3ab592 100644
--- a/src/security/detail/openssl.hpp
+++ b/src/security/detail/openssl.hpp
@@ -40,6 +40,6 @@
 #include <openssl/pem.h>
 #include <openssl/hmac.h>
 #include <openssl/x509.h>
-
+#include <openssl/err.h>
 
 #endif // NDN_SECURITY_DETAIL_OPENSSL_HPP