weka: 3.8.2 -> 3.9.2

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

This update was made based on information from https://repology.org/metapackage/weka/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 3.9.2 with grep in /nix/store/rv6aq5p1qacvpvaw9vszawzidsh8xdl9-weka-3.9.2
- directory tree listing: https://gist.github.com/c1ee16794a22549147d4d292cad986e5