poke and pingserver: use new signing API and helpers

refs #2919

Change-Id: I0770fc8ee553448f30b2e7a3ba902add441b9659
diff --git a/core/common.hpp b/core/common.hpp
index c2f833f..2b031cc 100644
--- a/core/common.hpp
+++ b/core/common.hpp
@@ -49,6 +49,8 @@
 #include <ndn-cxx/face.hpp>
 #include <ndn-cxx/interest.hpp>
 #include <ndn-cxx/security/key-chain.hpp>
+#include <ndn-cxx/security/signing-helpers.hpp>
+#include <ndn-cxx/security/signing-info.hpp>
 #include <ndn-cxx/util/scheduler.hpp>
 #include <ndn-cxx/util/signal.hpp>