Switch node traverser depending on php version
Switch node traverser depending on php version

This allows to use nicik/php-parser:^4 while supporting php < 7.

phpmetrics/PhpMetrics,UFOMelkor/PhpMetrics,Halleck45/PhpMetrics,UFOMelkor/PhpMetrics,phpmetrics/PhpMetrics,UFOMelkor/PhpMetrics,phpmetrics/PhpMetrics,Halleck45/PhpMetrics