Can't extend Analyzer class

[sunkan]

Hi

Thanks for an awesome library

Due to the use of static:: in

https://github.com/neomerx/cors-psr7/blob/0f968523b0b8215540915464aed08c5c4a4bf8b5/src/Analyzer.php#L277

Because the class constants are private they can't be accessed from the child class. And when you extend the analyzer it will automatically try to use the child scope when using static:: so it would work if you used self:: in the Analyzer class.

Would you be open to a pull-request to fix this?