message: Fix bug in documentation of  tf.while_loop.parallel_iterations
diff: @@ -2398,7 +2398,7 @@ def while_loop_v2(cond,
  ```python
  i = tf.constant(0)
  c = lambda i: tf.less(i, 10)
  - b = lambda i: tf.add(i, 1)
  + b = lambda i: (tf.add(i, 1), )
  r = tf.while_loop(c, b, [i])
  ```
  