clipgrab: 3.6.2 -> 3.6.8

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

This update was made based on information from https://repology.org/metapackage/clipgrab/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 3.6.8 with grep in /nix/store/1y989g5la7p05gizhmkbiq8k7c93yv27-clipgrab-3.6.8
- directory tree listing: https://gist.github.com/b319063218d7e4f46c8b6dccf8c9b79a