gnuplot: 5.2.2 -> 5.2.3

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

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

These checks were done:

- built on NixOS
- ran ‘/nix/store/3kixi49gqbpjnkrgdavmzkbsg7aaw51p-gnuplot-5.2.3/bin/gnuplot -h’ got 0 exit code
- ran ‘/nix/store/3kixi49gqbpjnkrgdavmzkbsg7aaw51p-gnuplot-5.2.3/bin/gnuplot --help’ got 0 exit code
- ran ‘/nix/store/3kixi49gqbpjnkrgdavmzkbsg7aaw51p-gnuplot-5.2.3/bin/.gnuplot-wrapped -h’ got 0 exit code
- ran ‘/nix/store/3kixi49gqbpjnkrgdavmzkbsg7aaw51p-gnuplot-5.2.3/bin/.gnuplot-wrapped --help’ got 0 exit code
- found 5.2.3 with grep in /nix/store/3kixi49gqbpjnkrgdavmzkbsg7aaw51p-gnuplot-5.2.3
- directory tree listing: https://gist.github.com/c09c0907f914e36a3f7c086d4b978dbf