fix an example in doc
fix an example in doc

ktnyt/chainer,hvy/chainer,okuta/chainer,tkerola/chainer,hvy/chainer,jnishi/chainer,jnishi/chainer,jnishi/chainer,pfnet/chainer,chainer/chainer,keisuke-umezawa/chainer,niboshi/chainer,chainer/chainer,ktnyt/chainer,ktnyt/chainer,wkentaro/chainer,jnishi/chainer,hvy/chainer,niboshi/chainer,ysekky/chainer,keisuke-umezawa/chainer,chainer/chainer,hvy/chainer,ronekko/chainer,ktnyt/chainer,wkentaro/chainer,rezoo/chainer,okuta/chainer,delta2323/chainer,keisuke-umezawa/chainer,okuta/chainer,aonotas/chainer,chainer/chainer,keisuke-umezawa/chainer,niboshi/chainer,kashif/chainer,okuta/chainer,wkentaro/chainer,wkentaro/chainer,anaruse/chainer,niboshi/chainer