PER-CS Code Highlighting Errors

[ravage84]

Going through the specification, I've noticed some of the (PHP) code highlighting to be somewhat off.

3. Declare Statements, Namespace, and Import Statements:

4.2 Using traits

10. Heredoc and Nowdoc:

[Jean85]

This is done in https://github.com/php-fig/www.php-fig.org/ using spatie/commonmark-highlighter: https://github.com/php-fig/www.php-fig.org/blob/d4e8ce81affa552f1b62da5fe3e35a802701710d/composer.json#L9

I'm moving this issue in that repo.

It's fairly new syntax, I don't know if that package supports that already (and we just have to upgrade it) or not...