Shorten the binding function of Array.grad
Shorten the binding function of Array.grad

jnishi/chainer,chainer/chainer,tkerola/chainer,hvy/chainer,hvy/chainer,pfnet/chainer,niboshi/chainer,keisuke-umezawa/chainer,niboshi/chainer,okuta/chainer,hvy/chainer,keisuke-umezawa/chainer,okuta/chainer,ktnyt/chainer,hvy/chainer,jnishi/chainer,niboshi/chainer,chainer/chainer,niboshi/chainer,wkentaro/chainer,chainer/chainer,jnishi/chainer,okuta/chainer,ktnyt/chainer,keisuke-umezawa/chainer,okuta/chainer,wkentaro/chainer,chainer/chainer,ktnyt/chainer,ktnyt/chainer,keisuke-umezawa/chainer,wkentaro/chainer,jnishi/chainer,wkentaro/chainer