fix doctest of function_hooks
fix doctest of function_hooks

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