minore bug fix in lines
minore bug fix in lines

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