DOCS: Update antora.yml to make 2019.9 the latest release
DOCS: Update antora.yml to make 2019.9 the latest release

Signed-off-by: Patrick Vacek <a38520cbbe2e974bc8b7ea86877dd3c7115ca2d7@gmail.com>

advancedtelematic/aktualizr,advancedtelematic/sota_client_cpp,advancedtelematic/aktualizr,advancedtelematic/sota_client_cpp,advancedtelematic/aktualizr,advancedtelematic/aktualizr