Add dev-only config to Natural Questions dataset
Great thanks ! I think we can fix the CI by copying the NQ folder on gcs to 0.0.3. Does that sound good ? I've copied the 0.0.2 folder content to 0.0.3, as suggested.

I'm updating the dataset card...
As suggested by @lhoestq and @thomwolf, a new config has been added to Natural Questions dataset, so that only dev split can be downloaded. 

Fix #413.