libyaml: 0.1.7 -> 0.2.1

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

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

These checks were done:

- built on NixOS

- 0 of 0 passed binary check by having a zero exit code.
- 0 of 0 passed binary check by having the new version present in output.
- found 0.2.1 with grep in /nix/store/bn221ypclyhac7pzicwf0kj7b6g03d4v-libyaml-0.2.1
- directory tree listing: https://gist.github.com/a183f8e1406cfb340cfc7e4809746583
- du listing: https://gist.github.com/6731d94c1363109427d6793cc7cd010a