Delete old versions of AppEngine instances to avoid the dreaded "Your app may not have more than 210 versions. Please delete one of the existing versions before trying to create a new version" error

First, let's do a dry-run. Run the following to keep 15 versions of each module around:

appengine-clean my-project-id 15 --dry-run

If you're happy with the result of the dry-run, let's delete:

appengine-clean my-project-id 15 --force