Add test for softplus
Add test for softplus

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