message: API docs: Fix usage example format in `to_categorical`.
diff: @@ -28,6 +28,7 @@ def to_categorical(y, num_classes=None, dtype='float32'):
  E.g. for use with categorical_crossentropy.
  Usage Example:
  +
  >>> y = [0, 1, 2, 3]
  >>> tf.keras.utils.to_categorical(y, num_classes=4)
  array([[1., 0., 0., 0.],
  