smplayer: 18.2.2 -> 18.3.0

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

This update was made based on information from https://repology.org/metapackage/smplayer/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 18.3.0 with grep in /nix/store/39n4zv5ynkjwhjcfs479fz6jj0pqfwvp-smplayer-18.3.0
- directory tree listing: https://gist.github.com/72db17f9f10b4ea51b5b470cfef842cf