stale entries not removed because lru is true by default

In `lookup` call handler for `cache_tab`:

```
{ok, Prio, Val} when (State#state.lru == true) or (Prio =< CleanPrio) ->
```

This means that stale entries can still be returned by default given:

```
%% Defaults
-define(MAX_SIZE, 1000).
-define(WARN, true).
-define(CACHE_MISSED, true).
-define(LRU, true).
-define(LIFETIME, 600). %% 10 minutes
```