Scale markers in a Vega group marker

https://cdnjs.cloudflare.com/ajax/libs/vega/3.0.0-beta.32/vega.js

https://cdnjs.cloudflare.com/ajax/libs/vega-lite/2.0.0-beta.3/vega-lite.js

https://cdnjs.cloudflare.com/ajax/libs/vega-embed/3.0.0-beta.14/vega-embed.js