message: update api in docstring example
diff: @@ -148,7 +148,7 @@ def bucket_by_sequence_length(element_length_func,
  ... lambda: elements, tf.int64, output_shapes=[None])
  >>> dataset = dataset.apply(
  - ... tf.data.experimental.bucket_by_sequence_length(
  + ... tf.data.bucket_by_sequence_length(
  ... element_length_func=lambda elem: tf.shape(elem)[0],
  ... bucket_boundaries=[3, 5],
  ... bucket_batch_sizes=[2, 2, 2]))
  @@ -175,7 +175,7 @@ def bucket_by_sequence_length(element_length_func,
  ... lambda: elements, tf.int32, output_shapes=[None])
  >>> dataset = dataset.apply(
  - ... tf.data.experimental.bucket_by_sequence_length(
  + ... tf.data.bucket_by_sequence_length(
  ... element_length_func=lambda elem: tf.shape(elem)[0],
  ... bucket_boundaries=[4, 7],
  ... bucket_batch_sizes=[2, 2, 2],
  @@ -205,7 +205,7 @@ def bucket_by_sequence_length(element_length_func,
  ... lambda: elements, tf.int32, output_shapes=[None])
  >>> dataset = dataset.apply(
  - ... tf.data.experimental.bucket_by_sequence_length(
  + ... tf.data.bucket_by_sequence_length(
  ... element_length_func=lambda elem: tf.shape(elem)[0],
  ... bucket_boundaries=[4, 7],
  ... bucket_batch_sizes=[2, 2, 2],
  