Can no longer be built

[robbiecarlton]

The nix env in this repo tries to download an archive of holo-nixpkgs. Holo-nixpkgs is no longer a public repo, so this fails.

Additionally, per @mjbrisebois, some of the libraries being used in this repo no longer work with recent rust tool chain, so it would probably be a good idea to bump the ed25519-dalek library at least, at the same time as updating the nix env

[mjbrisebois]

If you want to use rollup, the fastest solution might be to make a new repo using https://github.com/holochain/holochain-serialization-js as a template, change the cargo packages to what is needed, then use this key manager's rust code.