According to the composer.json file, this package requires php-5.4 version at least.
On require-dev setting, it requires phpunit/phpunit:^6.5 version. But this PHPUnit version requires php-7.0 version at least.
To fix above issue, I think it should let this package require php-7.2 or php-7.3 version because from php-5.4 to php-7.0 versions are too old/inactive.
According to the composer.json file, this package requires
php-5.4version at least.On
require-devsetting, it requiresphpunit/phpunit:^6.5version. But this PHPUnit version requiresphp-7.0version at least.To fix above issue, I think it should let this package require
php-7.2orphp-7.3version because fromphp-5.4tophp-7.0versions are too old/inactive.