Add cumprod to docs
Add cumprod to docs

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