fix udev rule for Ubuntu

udev didn't allow me to use this rule as-is, I had to add the leading 0 to the 0120. Maybe it wasn't optional in older versions of udev, I dunno, but this fixed it for me.

Discussion:
http://forum.yubico.com/viewtopic.php?f=33&t=1545&p=5991#p5991
http://forum.yubico.com/viewtopic.php?f=26&t=1535&p=5996#p5996
Merge pull request #4 from pushcx/master

fix udev rule for Ubuntu