Fix return types in next major version

[kelunik]

Methods to fix:

• \Amp\Beanstalk\BeanstalkClient::delete: return type hint is int but it returns bool (anyway this doesn't raise an error)
• \Amp\Beanstalk\BeanstalkClient::bury: return type hint is int but it returns bool (anyway this doesn't raise an error)
• \Amp\Beanstalk\BeanstalkClient::touch: return type hint is int but it returns bool (anyway this doesn't raise an error)

See #11.