libsass: 3.5.1 -> 3.5.2

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

This update was made based on information from https://repology.org/metapackage/libsass/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 3.5.2 with grep in /nix/store/nmrdgaid01pxdciii293qs8pj79a0jm1-libsass-3.5.2
- directory tree listing: https://gist.github.com/56876c4a3406ecb01ba31b9a9dbed572