Update composer.json

I've corrected the formatting and updated a couple of dependencies. As for phpunit, we don't need to specify 4.1 because `~4.0` means get any 4.x greater than 4.0.0, and `~4.1` means get any 4.x greater than 4.1.0. We don't actually require anything new in 4.1, so 4.0 as a minimum should be fine.