add l2 regularization to reduce fpe for machine translation english.
Created by: helinwang
Here is Chinese part by Longfei https://github.com/PaddlePaddle/book/pull/188 I will add English part.
Created by: helinwang
Here is Chinese part by Longfei https://github.com/PaddlePaddle/book/pull/188 I will add English part.