Correct Factory definition

Factory outputs a `Doctrine\DBAL\Connection` not a `StdClass`.

Without this change any validation of the container fails. I discovered this issue when using https://github.com/matthiasnoback/symfony-service-definition-validator/ to validate the container. 

I have a service where I typehint a setter with `Doctrine\DBAL\Connection`, but now validation fails because the `Definition` class reports that the factory outputs a `StdClass` when it does not.

ping @stof