extract scale so that ordinalOnlyField can have scale property too
extract scale so that ordinalOnlyField can have scale property too

ellisonbg/vega-lite,vega/vega-lite,ellisonbg/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,ellisonbg/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite