Fix comment in __nonzero__
Fix comment in __nonzero__

bayerj/chainer,okuta/chainer,jnishi/chainer,wkentaro/chainer,benob/chainer,delta2323/chainer,niboshi/chainer,wkentaro/chainer,jfsantos/chainer,AlpacaDB/chainer,keisuke-umezawa/chainer,benob/chainer,cemoody/chainer,chainer/chainer,hvy/chainer,sinhrks/chainer,elviswf/chainer,kiyukuta/chainer,hvy/chainer,truongdq/chainer,hidenori-t/chainer,anaruse/chainer,ktnyt/chainer,kuwa32/chainer,minhpqn/chainer,chainer/chainer,rezoo/chainer,sinhrks/chainer,muupan/chainer,AlpacaDB/chainer,tereka114/chainer,kikusu/chainer,wavelets/chainer,muupan/chainer,chainer/chainer,tkerola/chainer,niboshi/chainer,ytoyama/yans_chainer_hackathon,ktnyt/chainer,kikusu/chainer,1986ks/chainer,t-abe/chainer,ronekko/chainer,niboshi/chainer,sou81821/chainer,Kaisuke5/chainer,cupy/cupy,niboshi/chainer,cupy/cupy,aonotas/chainer,keisuke-umezawa/chainer,chainer/chainer,cupy/cupy,woodshop/chainer,hvy/chainer,pfnet/chainer,ktnyt/chainer,wkentaro/chainer,ikasumi/chainer,ysekky/chainer,tigerneil/chainer,okuta/chainer,yanweifu/chainer,tscohen/chainer,laysakura/chainer,ktnyt/chainer,keisuke-umezawa/chainer,masia02/chainer,hvy/chainer,t-abe/chainer,keisuke-umezawa/chainer,umitanuki/chainer,jnishi/chainer,jnishi/chainer,kashif/chainer,truongdq/chainer,okuta/chainer,woodshop/complex-chainer,wkentaro/chainer,jnishi/chainer,cupy/cupy,okuta/chainer