changed polylines color to white for black theme
changed polylines color to white for black theme

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