nspr: 4.18 -> 4.19

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

This update was made based on information from https://repology.org/metapackage/nspr/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 4.19 with grep in /nix/store/0gx5qa3iipnwiyaixnqgd4lljy70gqx8-nspr-4.19
- directory tree listing: https://gist.github.com/9813e84e7c71d6493cbe5b433f8f7f25