Keyboard controls on named radios don't work

[hasparus]

Just found a bug. Keyboard controls on radio inputs with "name" set don't work when "paper-radio" class is applied.

Steps to reproduce:

1. Go to https://www.getpapercss.com/docs/components/forms/
2. Focus one of radio inputs and try moving with keyboard arrows -- won't work.
3. Remove "paper-radio" class from radio inputs.
4. Now you can change your selection using keyboard.