Fix MarkModel model
Fix MarkModel model

ChakriCherukuri/bqplot,SylvainCorlay/bqplot,bloomberg/bqplot,dmadeka/bqplot,bloomberg/bqplot,SylvainCorlay/bqplot,SylvainCorlay/bqplot,ChakriCherukuri/bqplot,dmadeka/bqplot,bloomberg/bqplot,ChakriCherukuri/bqplot