Update dompdf & dependencies

Update dompdf & dependencies

DomPDF issues warnings on php 7.3
The latest version boasts 'Improved compatibility with PHP 7.3'
https://github.com/dompdf/dompdf/releases/tag/v0.8.3

To get there I needed to do
composer   update dompdf/dompdf phenx/php-svg-lib sabberworm/php-css-parser

& also got https://github.com/sabberworm/PHP-CSS-Parser/releases
onto the version that supports php 7+ - no obvious issues in the release notes  and

https://github.com/PhenX/php-svg-lib/releases
- moving us from Bruised Bumblebee to Fanatical Furet

Once againt nothing alarming & improved php 7+ support