Minor fix in the document
Minor fix in the document

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