bspwm: 0.9.3 -> 0.9.4

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

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

These checks were done:

- built on NixOS
- ran `/nix/store/w78rv4f7aq8nww3k2nmmkwfgl0mcqf60-bspwm-0.9.4/bin/bspwm -h` got 0 exit code
- ran `/nix/store/w78rv4f7aq8nww3k2nmmkwfgl0mcqf60-bspwm-0.9.4/bin/bspwm --help` got 0 exit code
- ran `/nix/store/w78rv4f7aq8nww3k2nmmkwfgl0mcqf60-bspwm-0.9.4/bin/bspwm --version` and found version 0.9.4
- ran `/nix/store/w78rv4f7aq8nww3k2nmmkwfgl0mcqf60-bspwm-0.9.4/bin/bspwm --help` and found version 0.9.4
- found 0.9.4 with grep in /nix/store/w78rv4f7aq8nww3k2nmmkwfgl0mcqf60-bspwm-0.9.4
- directory tree listing: https://gist.github.com/7ea8e79c97fb5b6594093a8d96aeb4e0