Add support for nikic/php-parser v5

Hello there,

I just tried installing this library but got the following error :

> o0h/ast-check-diff v1.0.0 requires nikic/php-parser ^4.16 -> found nikic/php-parser[v4.16.0, ..., v4.19.1] but the package is fixed to v5.1.0

Any chance an upgrade to be compatible with v5.x would be possible ?