Fix bug in Wealth of Nations example
Fix bug in Wealth of Nations example

SylvainCorlay/bqplot,ChakriCherukuri/bqplot,ssunkara1/bqplot,bloomberg/bqplot,bloomberg/bqplot,ssunkara1/bqplot,ChakriCherukuri/bqplot,dmadeka/bqplot,bloomberg/bqplot,dmadeka/bqplot,SylvainCorlay/bqplot,ChakriCherukuri/bqplot,SylvainCorlay/bqplot