“Content-Type: application/octet-stream” on downloading of invoice

Hi,

By using your plugin, I see when I download an invoice, Firefox wants open it with another application than my Pdf viewer.
I see the content-type is not “application/pdf”, but “application/octet-stream”.
In plugin source, I suspect the file wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-export.php:488 (I use the last version).

Thanks for the plugin,

R.