Ed25519 returns 5 instead of 6

[alessandrokonrad]

The CurveType enum returns 5 for Ed25519 as well as the the simplified builder::EdDSA25519Key class.
This is my result:

{1: 1, 3: -8, -1: 5, -2: h'D058ED6FA27CA8FA454F1BAF2AAC58EDB774531DD2813E7BC91600D3CA8F0D4B'}

[rooooooooob]

@alessandrokonrad thanks for noticing this in the CIP-30 discussion. I just put up a fix for this #10 - it was me doing the same thing I thought might be happening in the JS code, but it was in the rust details of Ed25519Key.

I think the ideal solution for these enums would be if we could fix wasm_bindgen to allow arbitrary/negative enum values, but I originally wasn't sure how hard it would be to do that or how long it would take to get that merged/etc. It's possible that if rustwasm/wasm-bindgen#2631 ever gets done that it would resolve this too, depending how they implement that.