message: Typo in backprop.py
diff: @@ -723,7 +723,7 @@ class GradientTape(object):
  with tf.GradientTape(watch_accessed_variables=False) as tape:
  tape.watch(variable_a)
  y = variable_a ** 2 # Gradients will be available for `variable_a`.
  - z = variable_b ** 3 # No gradients will be avaialble since `variable_b` is
  + z = variable_b ** 3 # No gradients will be available since `variable_b` is
  # not being watched.
  ```
  