Slightly optimize transpose_sequence
Slightly optimize transpose_sequence

kashif/chainer,pfnet/chainer,niboshi/chainer,cupy/cupy,keisuke-umezawa/chainer,aonotas/chainer,wkentaro/chainer,wkentaro/chainer,ronekko/chainer,tkerola/chainer,cupy/cupy,jnishi/chainer,okuta/chainer,jnishi/chainer,anaruse/chainer,niboshi/chainer,jnishi/chainer,hvy/chainer,chainer/chainer,keisuke-umezawa/chainer,ysekky/chainer,wkentaro/chainer,wkentaro/chainer,ktnyt/chainer,jnishi/chainer,rezoo/chainer,niboshi/chainer,chainer/chainer,okuta/chainer,keisuke-umezawa/chainer,kiyukuta/chainer,hvy/chainer,ktnyt/chainer,okuta/chainer,keisuke-umezawa/chainer,okuta/chainer,chainer/chainer,ktnyt/chainer,chainer/chainer,niboshi/chainer,ktnyt/chainer,delta2323/chainer,cupy/cupy,hvy/chainer,cupy/cupy,hvy/chainer