security: fix the compilation error of ValidatorConfig

Change-Id: I4740b316bfde1c164aa3251c3bd92563448b01b8
diff --git a/src/validator.hpp b/src/validator.hpp
index fd4bac8..abe957b 100644
--- a/src/validator.hpp
+++ b/src/validator.hpp
@@ -45,7 +45,7 @@
             const ndn::Name broadcastPrefix,
             const ndn::shared_ptr<ndn::CertificateCache>& cache,
             const int stepLimit = 10)
-    : ndn::ValidatorConfig(face, cache, stepLimit)
+    : ndn::ValidatorConfig(face, cache, ndn::ValidatorConfig::DEFAULT_GRACE_INTERVAL, stepLimit)
     , m_broadcastPrefix(broadcastPrefix)
   {
     m_broadcastPrefix.append("KEYS");