marp: 0.0.11 -> 0.0.12

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/marp/versions.

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 0.0.12 with grep in /nix/store/q8kib6qhxndj4hzscdzhgvnjkaxm4mbw-marp-0.0.12
- directory tree listing: https://gist.github.com/691bc668acd4e57a2cf187b6e1062f34