security: change enum to enum class in security-common.hpp

Change-Id: I5565c845cd57f3457c8120b11399a105fa83418d
Refs: #3083
diff --git a/src/security/signing-info.cpp b/src/security/signing-info.cpp
index 0872167..57cf046 100644
--- a/src/security/signing-info.cpp
+++ b/src/security/signing-info.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2013-2015 Regents of the University of California.
+ * Copyright (c) 2013-2016 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -33,7 +33,7 @@
                          const SignatureInfo& signatureInfo)
   : m_type(signerType)
   , m_name(signerName)
-  , m_digestAlgorithm(DIGEST_ALGORITHM_SHA256)
+  , m_digestAlgorithm(DigestAlgorithm::SHA256)
   , m_info(signatureInfo)
 {
 }