Support json media type for importing modules

[wrnrlr]

Dunno if this makes sense in a Deno context, but I've seen people do things like

import {version} from '../package.json'

but this fails:

error: An unsupported media type was attempted to be imported as a module.
  Specifier: https://raw.githubusercontent.com/wrnrlr/as-bind/master/package.json
  MediaType: Json

Same failure when importing local copy of same code.

[lucacasonato]

Duplicate of #7623