Set Publisher to "Digia Plc"

Use "Digia Plc" instead of bare "Qt" for the publisher.

Task-number: QTBUG-31138
Change-Id: Ief7f00b17d9ad686be5e2f1c8b4e7d7c207559f9
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>