Delete CNAME record when App is deleted
Currently, when an App specification contains a hostname managed by a DigitalOcean domain zone, a CNAME entry will be added pointing to the dynamically digitalocean.app generated hostname.
On removal of the App, the CNAME is left as a record entry in the managed zone. I have implemented an automatic deletion of the record as part of
appfile in PR https://github.com/renehernandez/appfile/pull/8, but I think that this is something that should be done natively by the API