Add missing import to cleanup function

Author: Szubie

ivis/ivis.py

@@ -22,6 +22,7 @@
 from .nn.losses import triplet_loss, is_categorical, is_multiclass, is_hinge
 from .nn.losses import semi_supervised_loss, validate_sparse_labels
 from .data.neighbour_retrieval import AnnoyKnnMatrix
+from .data.neighbour_retrieval.knn import cleanup_knn_index
 
 
 class Ivis(BaseEstimator):