please add nvidia-driver changes in r378360 to ports/UPDATING

[Anton Shterenlikht]

Hi

I think changes to x11/nvidia-driver* in r378360
need to be mentioned in ports/UPDATING.

Otherwise it's a POLA violation. nvidia-driver
no longer worked for me after the updated to 346.35.
I had to install nvidia-driver-340 instead.
But would be good to be warned about this change.

Thanks

Anton