libbitcoin-protocol: 3.4.0 -> 3.5.0

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 3.5.0 with grep in /nix/store/6726g0ccxn9iklg3vmpllmbp9dxkckgg-libbitcoin-protocol-3.5.0
- directory tree listing: https://gist.github.com/31ff5b959604c484f3e037bf19fbb0d9