At least, I suppose it was incorrect.  It won't build anywhere it has not
already built.  I don't know how it built where it already built.

overrides

They're not necessary on newly selected nixpkgs revision.

This format for the file can be generated automatically using something like:

  nix-prefetch-github \
    --nix \
    --rev $(git rev-parse HEAD) \
    PrivateStorageio ZKAPAuthorizer > /path/to/zkapauthorizer-repo.nix

run in in a checkout of ZKAPAuthorizer

Also bump the version being used.  This will be important in a minute.