message: Fix comment of bucket_by_sequence_length about return type of
  element_length_func. Current code requires tf.int32 in order to compare with
  buckets_min which is int32.
diff: @@ -108,7 +108,7 @@ def bucket_by_sequence_length(element_length_func,
  fraction of padding in a batch which increases training step efficiency.
  Args:
  - element_length_func: function from element in `Dataset` to `tf.int64`,
  + element_length_func: function from element in `Dataset` to `tf.int32`,
  determines the length of the element, which will determine the bucket it
  goes into.
  bucket_boundaries: `list<int>`, upper length boundaries of the buckets.
  