Possible fix for doctrine/migrations 2.0

[kbond]

I was testing #203 and found it still worked as expected with doctrine/migrations 1.1 but was getting an error when using doctrine/migrations 2.0.

The problem was $config->getMigrationsNamespace()/ $config->getMigrationsDirectory() are returning null and $diff->setMigrationsNamespace()/$diff->setMigrationsDirectory() can no longer accept null.

This PR fixed the issue for me but I'm not sure if there are other ramifications... I don't have a deep understanding on how the migration check works.

ping @stopfstedt, @jrjohnson

[jrjohnson]

Yes. I see that error and your fix works for me. Migrations check:

• [x] Errors when not all migrations are applied
• [x] Passes when they are

~I didn't have time today to dig any further into the why of your fix, but it does seem to work.~

Ah, I see. This change just uses the defaults, the same thing sending null used to do. Looks good to me.