* Drop support for PHP 5.4 and HHVM less than 3.18
* Update build process
* Update psysh
* Removed unused imports
* Fixed exception message for bad isset call
* Fixed isset handling
* Add PHP 8 to travis
* HHVM passes
* Always allow phpunit to be installed
* Updated deps
* Update SignatureFormatterTest.php
* Update ClassEnumeratorTest.php