Fix access level for generateForm method

In order to fix 

PHP Fatal error:  Access level to PUGX\GeneratorBundle\Command\GenerateDoctrineCrudCommand::generateForm() must be protected (as in class Sensio\Bundle\GeneratorBundle\Command\GenerateDoctrineCrudCommand) or weaker in /Volumes/Work Data/Projects/OscarRudilla/Store-SandBox/Application/Symfony/vendor/pugx/generator-bundle/PUGX/GeneratorBundle/Command/GenerateDoctrineCrudCommand.php on line 21