fix docstring
fix docstring

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