Check that the app logger has a driver() function, preventing fatal errors

[lvaneijden]

It appears that when the application logger is used and workers with a Redis connection are registered, it is assumed that the existing logger implements a 'driver' function, which then gets called for another method. Whenever a logger instance is attached that does not have the 'driver' function, the code breaks with a fatal error:
In QueueServiceProvider.php line 201:

Call to undefined method Monolog\Logger::driver()

Unsure of what the $resetScope callback is actually used for, I found that adding an additional check to see if the 'driver' function exists is small enough of a change that creating a new unit tests would be overkill. This pull request also does not break any currently running tests.

[taylorotwell]

The log binding in the container is a LogManager instance, which does have a driver method.

[lvaneijden]

But aren't applications able of overwriting this logger in some way? I'll have a look what my application has for sort of class bound to the 'log' register...but I don't see why we should not add this small patch in