clang-error: fix clang-diagnostic-inconsistent-missing-override error

This clang-error is generated when a function overrides a member
function but is not marked 'override'.

Change-Id: If27a9a75ae1d7b6112226e233db30421a02e8556
Signed-off-by: Pavithra Barithaya <pavithrabarithaya07@gmail.com>
diff --git a/item_updater.hpp b/item_updater.hpp
index 898b07c..59f9839 100644
--- a/item_updater.hpp
+++ b/item_updater.hpp
@@ -136,7 +136,7 @@
     /**
      * @brief Deletes all versions except for the current one
      */
-    void deleteAll();
+    void deleteAll() override;
 
     /** @brief Creates an active association to the
      *  newly active software image