update secp256k1-2019 w3id.org URLs to be versioned and consistent

[bnewbold]

I'm not sure if a small PR like this is a helpful way to contribute; I hope so! Don't think this gets anywhere near a "substantive contributions to specifications" but can do paperwork if needed.

The primary motivation here is that URL https://w3id.org/security/suites/secp256k1-2019 is valid, but does not point to an actual JSON-LD document, just a landing page which links to the v1 document. Most of the other URLs in the registry document point directly to the JSON-LD document.

For the secp256k1recovery-2020 URL, the href already has /v1, but the display URL does not. Seems like they should be consistent like the other URLs.

The background context which led me here was the https://didlint.ownyourdata.eu/validate tool wanting @context URLs to match what is in the spec registry document (which for secp256k1-2019 means no trailing /v1), while the @context should point directly to a JSON-LD doc, resulting in a contradiction.

Hypothetically it might be most correct to list multiple URLs in the "JSON-LD" columns in this document, both versioned and not.

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[bnewbold]

Gentle bump on this; can it be merged?

It looks like @mprorock (intentionally not mentioning) is no longer an editor in this repo, so won't be reviewing.