Bug when using `DoctrineDriver::countMessages()` with Postgresql

Because `visible` column is a bool, not an int.
The bug is present in the [0.x branch and last stable release](https://github.com/bernardphp/bernard/blob/0.x/src/Bernard/Driver/DoctrineDriver.php#L72), but it's [fixed on master branch](https://github.com/bernardphp/bernard/blob/master/src/Driver/Doctrine/Driver.php#L55)