message: Fix MarkDown formatting of code block.
diff: @@ -305,6 +305,7 @@ def implicit_val_and_grad(f):
  is not known ahead of time.
  Example:
  +
  ```python
  dense_layer = tf.layers.Dense(1)
  def loss(x, y):
  @@ -378,6 +379,7 @@ def implicit_grad(f):
  is not known ahead of time.
  Example:
  +
  ```python
  dense_layer = tf.layers.Dense(1)
  def loss(x, y):
  