events: Add missing memory header include

Include memory so we don't require a specific include ordering.

Change-Id: I2f5d195b07191963cb194de100ddf3523c295b93
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/occ_events.hpp b/occ_events.hpp
index cc6f616..26318e8 100644
--- a/occ_events.hpp
+++ b/occ_events.hpp
@@ -1,6 +1,8 @@
 #pragma once
 
 #include <systemd/sd-event.h>
+
+#include <memory>
 namespace open_power
 {
 namespace occ