message: Fix tf.train.piecewise_constant docstring example.
  The example currently implies that if the global_step is on the first boundary, it takes the second value, not the first. In reality, it takes the first value.
diff: @@ -103,8 +103,8 @@ def exponential_decay(learning_rate, global_step, decay_steps, decay_rate,
  def piecewise_constant(x, boundaries, values, name=None):
  """Piecewise constant from boundaries and interval values.
  - Example: use a learning rate that's 1.0 for the first 100000 steps, 0.5
  - for steps 100001 to 110000, and 0.1 for any additional steps.
  + Example: use a learning rate that's 1.0 for the first 100001 steps, 0.5
  + for the next 10000 steps, and 0.1 for any additional steps.
  ```python
  global_step = tf.Variable(0, trainable=False)
  