Fix typo in MixedMapDataset constructor docs.

PiperOrigin-RevId: 881035649

Author: agutkin

grain/_src/python/dataset/transformations/mix.py

@@ -90,7 +90,7 @@ def __init__(
       parents: Component datasets to draw from.
       proportions: Proportions from which to draw from each parent dataset.
         Defaults to uniform weight if selection_map is not given.
-      selection_map: Mapping from global index to paraent dataset and index
+      selection_map: Mapping from global index to parent dataset and index
         within parent dataset.
     """
     super().__init__(parents)