Add typecheck to negative_sampling
Add typecheck to negative_sampling

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