Upgrade to current version after initial migration.

I have an app that I built with a database initially, then subsequently added droid-migrate to. Migrations work fine with this.

If I uninstall, clear all data, and reinstall, then the following happens:

* `onCreate` is run, and therefore the `DBVersion1` migration is executed successfully
* `onUpgrade` is not called, and so subsequent migrations don't take place

I've attached a small patch that migrates up *after* creating the database initially.