adds role=radio to img alt=foo allowances

A `role=radio` was meant to be an allowance for an `img alt=foo`, but it had mistakenly been left out of the spec.
ARIA in HTML is fixing this oversight, w3c/html-aria#381, so this PR is to match this added allowance.

Author: scottaohara

lib/standards/html-elms.js

@@ -358,6 +358,7 @@ const htmlElms = {
           'menuitemradio',
           'option',
           'progressbar',
+					'radio',
           'scrollbar',
           'separator',
           'slider',