Load cached files rather than remote json

[symroe]

Hello from GDS in the UK, and thanks for making this :)

Sharing this as it might be helpful, but I'm not actually a Ruby dev, so it might be a shockingly bad way of doing things.

I've done a couple of things:

1. Removed hash-linker as it was causing problems with my data files, and it's redundant after;
2. Modified the cache to act more like I expected the cache to work: that is, to load files from the local directory, not the remote URL if it exists. To clear the cache, remove the files.

This change works for me, and might be useful to others too.