libbitcoin-explorer: 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
- ran `/nix/store/j07vd1p6h4c5fxyiskqqvfvi902vvsn2-libbitcoin-explorer-3.5.0/bin/bx help` got 0 exit code
- found 3.5.0 with grep in /nix/store/j07vd1p6h4c5fxyiskqqvfvi902vvsn2-libbitcoin-explorer-3.5.0
- directory tree listing: https://gist.github.com/672afbcda72ddef99aebfc49a81edc45