Simplify concatenate
Simplify concatenate

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