urlwatch: 2.11 -> 2.13

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

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

These checks were done:

- built on NixOS
- /nix/store/yxp495qcrnid39kivd5b748j8frqlkdm-urlwatch-2.13/bin/.urlwatch-wrapped passed the binary check.
- /nix/store/yxp495qcrnid39kivd5b748j8frqlkdm-urlwatch-2.13/bin/urlwatch passed the binary check.
- 2 of 2 passed binary check by having a zero exit code.
- 2 of 2 passed binary check by having the new version present in output.
- found 2.13 with grep in /nix/store/yxp495qcrnid39kivd5b748j8frqlkdm-urlwatch-2.13
- directory tree listing: https://gist.github.com/255d16f15c73bd3e1d6a677d1dd4c3c6
- du listing: https://gist.github.com/a3fa79092d3a5ca8f6929ee7b05f686f