Bug: Radio button don't show :focus state

> What MDL Version are you using? (please be specific, e.g. _major.minor.patch_)

1.3.0

> What browser(s) is this bug affecting (including version)?

Chrome 58.0.3029.81

> What OS (and version) are you using?

Linux - Ubuntu 16.04

> What are the steps to reproduce the bug? Can you create a plunker/codepen/jsfiddle which reproduces it?

Tab through to any radio button, they don't show any indication of being in focus, as defined [here](https://material.io/guidelines/components/selection-controls.html#selection-controls-radio-button).

The behaviour can be observed on the MDL website [here](https://getmdl.io/components/index.html#toggles-section/radio)

> What is the expected behavior?

The radio button in focus should have a light, wider ring around it (same as when pressed)

> What is the actual behavior?

No ring. The radio button shows the same behaviour as in default selected/un-selected state.

> Any other information you believe would be useful?

The checkboxes and switches, based on same base elements, do show the correct :focus behaviour. Only the radio buttons don't.