Fix document of split_axis
Fix document of split_axis

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