Get latest backup URL from heroku pg:backups (or pgbackups).

def get_file_url_for_heroku_app(self, source_app):
        """ Get latest backup URL from heroku pg:backups (or pgbackups). """
        self.print_message("Getting backup url for Heroku app '%s'" % source_app)
        args = [
            "heroku",
            "pg:backups:url",
            "--app=%s" % source_app,
        ]
        if self.args.use_pgbackups:
            args = [
                "heroku",
                "pgbackups:url",
                "--app=%s" % source_app,
            ]
        return subprocess.check_output(args).strip().decode('ascii')