ott: 0.27 -> 0.28

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

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

These checks were done:

- built on NixOS
- ran ‘/nix/store/2lbl8zpp2lrrh9pgh2gnyhimq6i86rl1-ott-0.28/bin/ott --help’ got 0 exit code
- ran ‘/nix/store/2lbl8zpp2lrrh9pgh2gnyhimq6i86rl1-ott-0.28/bin/ott.opt --help’ got 0 exit code
- found 0.28 with grep in /nix/store/2lbl8zpp2lrrh9pgh2gnyhimq6i86rl1-ott-0.28
- directory tree listing: https://gist.github.com/177f63b8c23bae6301ced29fb0e617c4