polyml: 5.7 -> 5.7.1

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

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

These checks were done:

- built on NixOS
- ran `/nix/store/ac6iwd3ixncb9cqjg59fbj2nzcfmsqgn-polyml-5.7.1/bin/poly --help` got 0 exit code
- ran `/nix/store/ac6iwd3ixncb9cqjg59fbj2nzcfmsqgn-polyml-5.7.1/bin/poly -v` and found version 5.7.1
- ran `/nix/store/ac6iwd3ixncb9cqjg59fbj2nzcfmsqgn-polyml-5.7.1/bin/poly --help` and found version 5.7.1
- ran `/nix/store/ac6iwd3ixncb9cqjg59fbj2nzcfmsqgn-polyml-5.7.1/bin/polyc --help` got 0 exit code
- ran `/nix/store/ac6iwd3ixncb9cqjg59fbj2nzcfmsqgn-polyml-5.7.1/bin/polyc --help` and found version 5.7.1
- found 5.7.1 with grep in /nix/store/ac6iwd3ixncb9cqjg59fbj2nzcfmsqgn-polyml-5.7.1
- directory tree listing: https://gist.github.com/e23988ea219cf9deddb7b7c0578cfd89