buku: 3.6 -> 3.7

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

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

These checks were done:

- built on NixOS
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/.buku-wrapped -h` got 0 exit code
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/.buku-wrapped --help` got 0 exit code
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/.buku-wrapped -h` and found version 3.7
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/.buku-wrapped --help` and found version 3.7
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/buku -h` got 0 exit code
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/buku --help` got 0 exit code
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/buku -h` and found version 3.7
- ran `/nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7/bin/buku --help` and found version 3.7
- found 3.7 with grep in /nix/store/xhqxppgivy66mf4v46acf4p9qzqrnfhs-buku-3.7
- directory tree listing: https://gist.github.com/231e0667743da0993083d1dd37c787b7