Declaration of Codeception\Specify\ResultPrinter::writeProgress($progress): void should be compatible with PHPUnit\TextUI\ResultPrinter::writeProgress(string $progress): void
This is due to incompatible versions of Specify/PHPUnit, not a lack of PHP7 support. Double check that you're using a supported version of PHPUnit with your version of Specify.
In ResultPrinter.php line 24:
Declaration of Codeception\Specify\ResultPrinter::writeProgress($progress): void should be compatible with PHPUnit\TextUI\ResultPrinter::writeProgress(string $progress): void