Fix copy method
Fix copy method

ronekko/chainer,niboshi/chainer,hvy/chainer,hvy/chainer,anaruse/chainer,keisuke-umezawa/chainer,ktnyt/chainer,niboshi/chainer,okuta/chainer,aonotas/chainer,tkerola/chainer,wkentaro/chainer,okuta/chainer,wkentaro/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,okuta/chainer,wkentaro/chainer,pfnet/chainer,wkentaro/chainer,ktnyt/chainer,jnishi/chainer,chainer/chainer,jnishi/chainer,niboshi/chainer,chainer/chainer,jnishi/chainer,hvy/chainer,niboshi/chainer,chainer/chainer,ktnyt/chainer,rezoo/chainer,ktnyt/chainer,okuta/chainer,chainer/chainer,keisuke-umezawa/chainer,hvy/chainer,jnishi/chainer