management+util: add 'override' specifier where applicable

Change-Id: Iafb9c2c59026e4268522120f405585ba35fac248
diff --git a/src/util/in-memory-storage-persistent.hpp b/src/util/in-memory-storage-persistent.hpp
index 3cd12ef..3265f52 100644
--- a/src/util/in-memory-storage-persistent.hpp
+++ b/src/util/in-memory-storage-persistent.hpp
@@ -38,9 +38,6 @@
   explicit
   InMemoryStoragePersistent(boost::asio::io_service& ioService);
 
-  virtual
-  ~InMemoryStoragePersistent();
-
 NDN_CXX_PUBLIC_WITH_TESTS_ELSE_PROTECTED:
   /** @brief Do nothing.
    *
@@ -49,7 +46,7 @@
    *  @return false
    */
   virtual bool
-  evictItem();
+  evictItem() override;
 };
 
 } // namespace util