Update testing matrix
Update testing matrix

- php7.0 is no longer supported on master
- php7.3 is now supported on master

Signed-off-by: Joas Schilling <ab43a7c9cb5b2380afc4ddf8b3e2583169b39a02@schilljs.com>

nextcloud/spreed,nextcloud/spreed,nextcloud/spreed