Incompatible with PHPUnit 6

[JDGrimes]

Running against PHPUnit 6 gives this error:

$ phpunit
PHP Fatal error:  Class 'PHPUnit_Util_Getopt' not found in /Users/johngrimes/git/wordpoints/vendor/jdgrimes/wpppb/src/WPPPB/Util/GetOpt.php on line 15
PHP Stack trace:
PHP   1. {main}() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/phpunit:0
PHP   2. PHPUnit\TextUI\Command::main() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/phpunit:53
PHP   3. PHPUnit\TextUI\Command->run() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/src/TextUI/Command.php:148
PHP   4. PHPUnit\TextUI\Command->handleArguments() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/src/TextUI/Command.php:159
PHP   5. PHPUnit\TextUI\Command->handleBootstrap() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/src/TextUI/Command.php:788
PHP   6. PHPUnit\Util\Fileloader::checkAndLoad() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/src/TextUI/Command.php:991
PHP   7. PHPUnit\Util\Fileloader::load() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/src/Util/Fileloader.php:48
PHP   8. include_once() /Users/johngrimes/git/wordpoints/vendor/phpunit/phpunit/src/Util/Fileloader.php:64
PHP   9. WordPoints_PHPUnit_Bootstrap_Loader::instance() /Users/johngrimes/git/wordpoints/dev-lib/phpunit/includes/bootstrap.php:92
PHP  10. WordPoints_PHPUnit_Bootstrap_Loader->__construct() /Users/johngrimes/git/wordpoints/dev-lib/phpunit/classes/bootstrap/loader.php:74
PHP  11. WordPoints_PHPUnit_Bootstrap_Loader->__construct() /Users/johngrimes/git/wordpoints/dev-lib/phpunit/classes/bootstrap/loader.php:90
PHP  12. WordPoints_PHPUnit_Bootstrap_Loader->should_install_plugins() /Users/johngrimes/git/wordpoints/vendor/jdgrimes/wpppb/src/WPPPB/Loader.php:81
PHP  13. WordPoints_PHPUnit_Bootstrap_Loader->should_install_plugins() /Users/johngrimes/git/wordpoints/dev-lib/phpunit/classes/bootstrap/loader.php:349
PHP  14. WordPoints_PHPUnit_Bootstrap_Loader->running_uninstall_tests() /Users/johngrimes/git/wordpoints/vendor/jdgrimes/wpppb/src/WPPPB/Loader.php:251
PHP  15. WordPoints_PHPUnit_Bootstrap_Loader->running_uninstall_tests() /Users/johngrimes/git/wordpoints/dev-lib/phpunit/classes/bootstrap/loader.php:390
PHP  16. spl_autoload_call() /Users/johngrimes/git/wordpoints/vendor/jdgrimes/wpppb/src/WPPPB/Loader.php:273
PHP  17. Composer\Autoload\ClassLoader->loadClass() /Users/johngrimes/git/wordpoints/vendor/jdgrimes/wpppb/src/WPPPB/Loader.php:273
PHP  18. Composer\Autoload\includeFile() /Users/johngrimes/git/wordpoints/vendor/composer/ClassLoader.php:322
PHP  19. include() /Users/johngrimes/git/wordpoints/vendor/composer/ClassLoader.php:444

Since WordPress already includes a shim, we should be able to just load that shim earlier, and that should fix the issue.