message: Fix blank_index docstring
diff: @@ -314,7 +314,7 @@ def ctc_greedy_decoder(inputs,
  sequence_length: 1-D `int32` vector containing sequence lengths, having size
  `[batch_size]`.
  merge_repeated: Boolean. Default: True.
  - blank_index: (optional) Set the class index to use for the blank label.
  + blank_index: (Optional). Default: -1. The class index to use for the blank label.
  Negative values will start from num_classes, ie, -1 will reproduce the
  ctc_greedy_decoder behavior of using num_classes - 1 for the blank symbol,
  which, actually, corresponds to the default.
  