message: fix spelling error
  fix spelling error for documents.
diff: @@ -828,7 +828,7 @@ class BaseSession(SessionInterface):
  nested list, tuple, namedtuple, dict, or OrderedDict containing graph
  elements at its leaves. A graph element can be one of the following types:
  - * An `tf.Operation`.
  + * A `tf.Operation`.
  The corresponding fetched value will be `None`.
  * A `tf.Tensor`.
  The corresponding fetched value will be a numpy ndarray containing the
  