publish heroku should default to currently tagged version

[simonw]

Had a report that deploying to Heroku was using the previously installed version of Datasette, not the latest.

Could be because of this:

datasette/datasette/publish/heroku.py

Lines 172 to 179 in af6c6c5

	if branch:
	install = [
	"https://github.com/simonw/datasette/archive/{branch}.zip".format(
	branch=branch
	)
	] + list(install)
	else:
	install = ["datasette"] + list(install)

Heroku documentation recommends pinning to specific versions https://devcenter.heroku.com/articles/python-pip

So... we could ensure we default to an install value of ["datasette>=current_tag"].

[simonw]

Trickiness here is what tag to use. Do we use the tag of the installed copy of Datasette that is running datasette publish? That would mean you don't get the latest features in your deployed release.

Could hit an API to figure out the most recent version? Bit odd.

Could we output the version of Datasette that was deployed and tell people they can run --latest to force the most recent release?