Replace Mark Type with Mark in the doc layout @domoritz
Replace Mark Type with Mark in the doc layout @domoritz

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