Error when invoking WikiGraphCheckOrphans

```
Error detected while processing function wiki#graph#check_orphans:

line    5:
E716: Key not present in Dictionary: "refresh_cache"
```
Not have a lot of clues, default config for everything.

Reproduced on :
  - OpenBSD (manual repos clone)
  - Termux (Paq manager)

Thanks for your wonderful plugin.