message: Adding space before doctest per review
diff: @@ -983,6 +983,7 @@ def is_tensor(x): # pylint: disable=invalid-name
  can be converted to a tensor using `ops.convert_to_tensor(x)`.
  Usage example:
  +
  >>> tf.is_tensor(tf.constant([[1,2,3],[4,5,6],[7,8,9]]))
  True
  >>> tf.is_tensor("Hello World")
  