Update TagBot.yml to current best practice #13

	# remove PR previews once they're merged
	# <https://juliadocs.github.io/Documenter.jl/dev/man/hosting/#gh-pages-Branch>
	name: Doc Preview Cleanup
	on:
	pull_request:
	types: [closed]
	jobs:
	doc-preview-cleanup:
	runs-on: ubuntu-latest
	steps:
	- name: Checkout gh-pages branch
	uses: actions/checkout@v2
	with:
	ref: gh-pages
	- name: Delete preview and history + push changes
	run: \|
	if [ -d "previews/PR$PRNUM" ]; then
	git config user.name "Documenter.jl"
	git config user.email "[email protected]"
	git rm -rf "previews/PR$PRNUM"
	git commit -m "delete preview"
	git branch gh-pages-new $(echo "delete history" \| git commit-tree HEAD^{tree})
	git push --force origin gh-pages-new:gh-pages
	fi
	env:
	PRNUM: ${{ github.event.number }}

Provide feedback