Bump the default version argument in `use_data()` to 3

[Tim Taylor]

Now we're a few years past the R 3.6 release is it worth bumping the default version argument for use_data() from 2 to 3 (matching R's current default)?

[Jennifer (Jenny) Bryan]

@hadley I think it might be time to do this. Do you have any reservations?

[Hadley Wickham]

@jennybc agreed. I think it's time.