message: Fixes markdown formatting of EstimatorSpec constructor.
  Before, it was rendering as italics because of the missing newline.
diff: @@ -77,6 +77,7 @@ class EstimatorSpec(
  """Creates a validated `EstimatorSpec` instance.
  Depending on the value of `mode`, different arguments are required. Namely
  +
  * For `mode == ModeKeys.TRAIN`: required fields are `loss` and `train_op`.
  * For `mode == ModeKeys.EVAL`: required field is `loss`.
  * For `mode == ModeKeys.PREDICT`: required fields are `predictions`.
  