Update contribution.rst
Update contribution.rst
keisuke-umezawa/chainer,ktnyt/chainer,wkentaro/chainer,niboshi/chainer,keisuke-umezawa/chainer,wkentaro/chainer,wkentaro/chainer,pfnet/chainer,hvy/chainer,hvy/chainer,chainer/chainer,okuta/chainer,jnishi/chainer,ktnyt/chainer,okuta/chainer,tkerola/chainer,hvy/chainer,chainer/chainer,keisuke-umezawa/chainer,niboshi/chainer,jnishi/chainer,niboshi/chainer,wkentaro/chainer,okuta/chainer,chainer/chainer,chainer/chainer,ktnyt/chainer,okuta/chainer,ktnyt/chainer,hvy/chainer,jnishi/chainer,niboshi/chainer,keisuke-umezawa/chainer,jnishi/chainer