sfml: 2.4.2 -> 2.5.0

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

This update was made based on information from https://repology.org/metapackage/sfml/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 2.5.0 with grep in /nix/store/j708rilms5fpihj454xv4m8yph07v3y5-sfml-2.5.0
- directory tree listing: https://gist.github.com/2efaabd811738a49adb17b7c96980837