Missing return type in execute() in fixtures loader

[tacman]

PHP Fatal error: Declaration of Doctrine\Bundle\FixturesBundle\Command\LoadDataFixturesDoctrineCommand::execute(Symfony\Component\Console\Input\InputInterface $input, Symfony\Component\Console\Output\OutputInterface $output) must be compatible with Symfony\Component\Console\Command\Command::execute(Symfony\Component\Console\Input\InputInterface $input, Symfony\Component\Console\Output\OutputInterface $output): int in /home/tac/g/tacman/symfony-demo/vendor/doctrine/doctrine-fixtures-bundle/Command/LoadDataFixturesDoctrineCommand.php on line 99

I'll submit a PR now.