pingserver: sign with DigestSha256

refs #2700

Change-Id: I119ddce4ae256ccf9a5b5731d00c705e6a0f1ed8
diff --git a/tools/ping/server/ping-server.cpp b/tools/ping/server/ping-server.cpp
index e0d0beb..699da5b 100644
--- a/tools/ping/server/ping-server.cpp
+++ b/tools/ping/server/ping-server.cpp
@@ -66,7 +66,7 @@
   shared_ptr<Data> data = make_shared<Data>(interestName);
   data->setFreshnessPeriod(m_options.freshnessPeriod);
   data->setContent(m_payload);
-  m_keyChain.sign(*data);
+  m_keyChain.signWithSha256(*data);
   m_face.put(*data);
 
   ++m_nPings;