message: Update momentum.py
  fix docstring line lengths
diff: @@ -60,9 +60,10 @@ class MomentumOptimizer(optimizer.Optimizer):
  variable(s) passed to the optimizer. Using Nesterov Momentum makes the
  variable(s) track the values called `theta_t + mu*v_t` in the paper.
  This implementation is an approximation of the original formula, valid
  - for high values of momentum. It will compute the "adjusted gradient" in NAG
  - by assuming that the new gradient will be estimated by the current
  - average gradient plus the product of momentum and the change in the average gradient.
  + for high values of momentum. It will compute the "adjusted gradient"
  + in NAG by assuming that the new gradient will be estimated by the
  + current average gradient plus the product of momentum and the change
  + in the average gradient.
  @compatibility(eager)
  When eager execution is enabled, `learning_rate` and `momentum` can each be
  