Update `cache` argument in docs

[OmeGak]

The image_cache option specified in the documentation is not correct. The correct option is cache. Using image_cache leads to no cache being applied at all, as the option is completely ignored without warning. It would be useful to fail when passing invalid options, to avoid them silently not being applied.

[liZe]

The image_cache option specified in the documentation is not correct.

Thank you!

It would be useful to fail when passing invalid options, to avoid them silently not being applied.

Yes, it would be useful. Comparing the options keys to the ones in DEFAULT_OPTIONS in render should work.

[liZe]

Thanks!

[OmeGak]

It was my pleasure! 🙏