libsigrokdecode: 0.5.0 -> 0.5.1

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

This update was made based on information from https://repology.org/metapackage/libsigrokdecode/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 0.5.1 with grep in /nix/store/bzy46mv9yqpqap2swy9gc25x0hdbq1ny-libsigrokdecode-0.5.1
- directory tree listing: https://gist.github.com/4794e65a1bf494e590272e83866d9e95