snd: 18.2 -> 18.3

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

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

These checks were done:

- built on NixOS
- ran ‘/nix/store/18mdi0m90asngnmnf313bbkpyyzjs96b-snd-18.3/bin/snd --help’ got 0 exit code
- found 18.3 with grep in /nix/store/18mdi0m90asngnmnf313bbkpyyzjs96b-snd-18.3
- directory tree listing: https://gist.github.com/3e3d90a56bba746c97163a9bc00919f2