Fix hstack
Fix hstack

use cupy function

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