Update fio.json

the Fio doesn't have a USB chip (done via [external FTDI](http://arduino.cc/en/Main/ArduinoBoardFioProgramming)), propose representing this in data via `null`s for `pid` and `vid`
Merge pull request #10 from PixnBits/master

+vid/pid to mega2560 & uno (#7)
Merge pull request #9 from PixnBits/patch-1

Update fio.json