fix: update clean command to take account of the keep_files option (#10007)
This is a 🐛 bug fix.
<!--
Before you submit this pull request, make sure to have a look at the
following
checklist. If you don't know how to do some of these, that's fine!
Submit
your pull request and we will help you out on the way.
- I've added tests (if it's a bug, feature or enhancement)
- ...
Click on the "Follow" button below and you'll get the latest news from Recent Commits to jekyll:master via email, mobile or you can read them on your personal news page on this site.
You can unsubscribe anytime you want easily.
You can also choose the topics or keywords that you're interested in, so you receive only what you want.
Recent Commits to jekyll:master title: GitHub · Change is constant. GitHub keeps you ahead. · GitHub