Update train_loop.rst
Update train_loop.rst

#4696
rezoo/chainer,wkentaro/chainer,okuta/chainer,hvy/chainer,ktnyt/chainer,ktnyt/chainer,anaruse/chainer,hvy/chainer,jnishi/chainer,wkentaro/chainer,ktnyt/chainer,okuta/chainer,jnishi/chainer,jnishi/chainer,okuta/chainer,keisuke-umezawa/chainer,chainer/chainer,chainer/chainer,ktnyt/chainer,keisuke-umezawa/chainer,niboshi/chainer,tkerola/chainer,niboshi/chainer,keisuke-umezawa/chainer,niboshi/chainer,keisuke-umezawa/chainer,hvy/chainer,okuta/chainer,chainer/chainer,wkentaro/chainer,jnishi/chainer,wkentaro/chainer,hvy/chainer,chainer/chainer,ronekko/chainer,pfnet/chainer,niboshi/chainer