Fix missing import.
Fix missing import.

This fixes deleting a lasso around a line.
SylvainCorlay/bqplot,ChakriCherukuri/bqplot,dmadeka/bqplot,ssunkara1/bqplot,bloomberg/bqplot,ssunkara1/bqplot,ChakriCherukuri/bqplot,dmadeka/bqplot,bloomberg/bqplot,ChakriCherukuri/bqplot,SylvainCorlay/bqplot,bloomberg/bqplot,SylvainCorlay/bqplot