Fixes atcommand killmonster2 bypass

* Atcommand killmonster2 would make monsters drop items because of a case insensitive check.
Thanks to @Mamb0w!

src/map/atcommand.cpp

@@ -2283,7 +2283,7 @@ ACMD_FUNC(killmonster)
 
 	parent_cmd = atcommand_alias_db.checkAlias(command+1);
 
-	drop_flag = strcmp(parent_cmd, "killmonster2");
+	drop_flag = strcmpi(parent_cmd, "killmonster2");
 
 	map_foreachinmap(atkillmonster_sub, map_id, BL_MOB, -drop_flag);