security: add missing virtual destructor to Validator base class

Change-Id: I4a5aac178c3b61fdb898fdffe67f9271a37e729d
diff --git a/src/security/validator.cpp b/src/security/validator.cpp
index 1ef7a05..ffb9501 100644
--- a/src/security/validator.cpp
+++ b/src/security/validator.cpp
@@ -42,6 +42,8 @@
 {
 }
 
+Validator::~Validator() = default;
+
 void
 Validator::validate(const Interest& interest,
                     const OnInterestValidated& onValidated,