Update URL and image

[jrfnl]

PHP_CodeSniffer is under new management. See: squizlabs/PHP_CodeSniffer#3932

Please update the URL in the project description to https://github.com/PHPCSStandards/PHP_CodeSniffer/

Would also be good to update the Docker image as the current version of PHPCS is 3.9.1, while this Docker image appears to use v 3.5.8.
Oh and probably also a good idea to upgrade from using Composer 1.x to 2.x.

[jrfnl]

Oh and the same probably also goes for https://github.com/phpqa/phpcbf/