Fix docstring of black_out
Fix docstring of black_out

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