Arduino LMIC library updated

@matthijs: I just joined a Ideetron Nexus with OTAA using your library without much trouble (once I figured out which bits go where, reversed or not), so that seems to be working (in case you didn't know yet).

Had to DISABLE_PING and/or DISABLE_BEACONS to fit it in the Nexus.

And getting non-zero FCntUp in ttnctl devices info

Edit: downlink works, too!