Fix slots in vertical USB package to match oshpark requirements

Fix slots in vertical USB package to match oshpark requirements

oshpark wants two holes, one at either end, with copper painted around
them on both sides. I've done this by making round-end pads that go
from hole to hole. When you use this package, make sure you paint a
19.68mil trace in the outline layer between the holes; I can't see any
way to get that into the package.

Signed-off-by: Keith Packard <keithp@keithp.com>