Fix document of to_gpu
Fix document of to_gpu

wkentaro/chainer,ktnyt/chainer,chainer/chainer,benob/chainer,okuta/chainer,sinhrks/chainer,ysekky/chainer,wkentaro/chainer,t-abe/chainer,muupan/chainer,pfnet/chainer,niboshi/chainer,delta2323/chainer,keisuke-umezawa/chainer,cemoody/chainer,okuta/chainer,okuta/chainer,truongdq/chainer,jnishi/chainer,kikusu/chainer,jnishi/chainer,hvy/chainer,chainer/chainer,keisuke-umezawa/chainer,niboshi/chainer,kashif/chainer,rezoo/chainer,keisuke-umezawa/chainer,ktnyt/chainer,jnishi/chainer,sinhrks/chainer,niboshi/chainer,cupy/cupy,ktnyt/chainer,chainer/chainer,hvy/chainer,AlpacaDB/chainer,kiyukuta/chainer,anaruse/chainer,muupan/chainer,cupy/cupy,AlpacaDB/chainer,wkentaro/chainer,benob/chainer,ronekko/chainer,wkentaro/chainer,tkerola/chainer,keisuke-umezawa/chainer,jnishi/chainer,niboshi/chainer,kikusu/chainer,ktnyt/chainer,hvy/chainer,chainer/chainer,t-abe/chainer,cupy/cupy,aonotas/chainer,cupy/cupy,okuta/chainer,hvy/chainer,truongdq/chainer