Document: `EvolutionChain.region` and `EvolutionChain.base_form` does not exist

[RamType0]

Steps to Reproduce:

1. See document to ensure that EvolutionChain.region and EvoluionChain.base_form is defined.
2. Access https://pokeapi.co/api/v2/evolution-chain/24/
3. They actually does not exist. Instead of these, it have region_id and base_form_id.

[jemarq04]

I had also added that to the documentation recently, thanks for catching that. I believe that may actually be a problem with how region_id and base_form_id are implemented - for consistency, it should be just region and base_form when the endpoints are created. Other fields in the CSV have _id at the end, but the actual field in the endpoint has that omitted (e.g. trade_species_id -> trade_species).

I was planning on looking through to make sure data was up-to-date for those fields, so I'll be sure to link this when I make a PR.