Move seq_expand to nn.py.
Move seq_expand to nn.py.

putcn/Paddle,baidu/Paddle,QiJune/Paddle,jacquesqiao/Paddle,luotao1/Paddle,tensor-tang/Paddle,baidu/Paddle,chengduoZH/Paddle,chengduoZH/Paddle,jacquesqiao/Paddle,putcn/Paddle,jacquesqiao/Paddle,luotao1/Paddle,Canpio/Paddle,QiJune/Paddle,putcn/Paddle,putcn/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,chengduoZH/Paddle,baidu/Paddle,QiJune/Paddle,baidu/Paddle,PaddlePaddle/Paddle,Canpio/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,Canpio/Paddle,Canpio/Paddle,pkuyym/Paddle,lcy-seso/Paddle,pkuyym/Paddle,QiJune/Paddle,reyoung/Paddle,jacquesqiao/Paddle,tensor-tang/Paddle,tensor-tang/Paddle,chengduoZH/Paddle,lcy-seso/Paddle,putcn/Paddle,Canpio/Paddle,reyoung/Paddle,lcy-seso/Paddle,pkuyym/Paddle,PaddlePaddle/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,lcy-seso/Paddle,reyoung/Paddle,tensor-tang/Paddle,jacquesqiao/Paddle,luotao1/Paddle,pkuyym/Paddle,PaddlePaddle/Paddle,QiJune/Paddle,tensor-tang/Paddle,luotao1/Paddle,reyoung/Paddle,Canpio/Paddle,Canpio/Paddle,QiJune/Paddle,baidu/Paddle,lcy-seso/Paddle,pkuyym/Paddle,Canpio/Paddle,lcy-seso/Paddle,jacquesqiao/Paddle,pkuyym/Paddle,chengduoZH/Paddle,luotao1/Paddle,putcn/Paddle