message: Correct the formulation in the description of the centered rmsprop
diff: @@ -30,7 +30,7 @@ This implementation of RMSProp uses plain momentum, not Nesterov momentum.
  The centered version additionally maintains a moving (discounted) average of the
  gradients, and uses that average to estimate the variance:
  -mean_grad = decay * mean_square{t-1} + (1-decay) * gradient
  +mean_grad = decay * mean_grad{t-1} + (1-decay) * gradient
  mean_square = decay * mean_square{t-1} + (1-decay) * gradient ** 2
  mom = momentum * mom{t-1} + learning_rate * g_t /
  sqrt(mean_square - mean_grad**2 + epsilon)
  