message: Fix small typo and tweak wording in TensorBoard callback doc.
diff: @@ -1118,9 +1118,9 @@ class TensorBoard(Callback):
  ValueError: If histogram_freq is set and no validation data is provided.
  @compatibility(eager)
  - Using `Tensorboard` callback will work while eager execution is enabled,
  - however outputting histogram summaries of weights and gradients is not
  - supported, and thus `histogram_freq` will be ignored.
  + Using the `TensorBoard` callback will work when eager execution is enabled,
  + with the restriction that outputting histogram summaries of weights and
  + gradients is not supported. Consequently, `histogram_freq` will be ignored.
  @end_compatibility
  """
  