JSON and YAML versions are often out of sync

[jviotti]

For example, the 0.18 versions have the following discrepancy that causes bundling to fail:

https://github.com/apis-json/api-json/blob/develop/spec/schema_0.18.json#L334

        "$ref": "#/definitions/urls"

https://github.com/apis-json/api-json/blob/develop/spec/schema_0.18.yml#L252

        $ref: "#/$defs/urls"

The former is invalid, as definitions doesn't exist there.

I suggest only offering a single format. Whatever you prefer. For OpenAPI folks, maybe YAML is nicer.

Things like my registry will at some point provide a way to get the schemas in multiple formats for the ones that need it!