add missing import

Author: Matt Sokoloff

labelbox/data/serialization/ndjson/label.py

@@ -1,4 +1,5 @@
 from itertools import groupby
+
 from labelbox.data.annotation_types.metrics import ScalarMetric
 
 from operator import itemgetter
@@ -12,6 +13,7 @@
 from ...annotation_types.data import ImageData, TextData, VideoData
 from ...annotation_types.label import Label
 from ...annotation_types.ner import TextEntity
+from ...annotation_types.classification import Dropdown
 from .metric import NDScalarMetric, NDMetricAnnotation
 from .classification import NDChecklistSubclass, NDClassification, NDClassificationType, NDRadioSubclass
 from .objects import NDObject, NDObjectType