Bump markdownlint version to 0.13.0
Markdownlint was behaving a little differently locally and I realize it's because it's using a different version. Some minor improvements. The main thing that's nice is more detailed error messages.
I've been using it locally for a few weeks and I've not had any issues, so I'd like to bump it.
https://github.com/DavidAnson/markdownlint-cli2/blob/main/CHANGELOG.md#0130