oniguruma: 6.6.1 -> 6.7.1

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. 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 6.7.1 with grep in /nix/store/adypaqqfpnmali0662725r7xdzgyqqh0-onig-6.7.1
- directory tree listing: https://gist.github.com/b40671987a847be6597a16cb977ff6a4