adjust eps for fp16
adjust eps for fp16

hvy/chainer,keisuke-umezawa/chainer,okuta/chainer,chainer/chainer,pfnet/chainer,wkentaro/chainer,okuta/chainer,keisuke-umezawa/chainer,chainer/chainer,niboshi/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,wkentaro/chainer,niboshi/chainer,okuta/chainer,chainer/chainer,niboshi/chainer,hvy/chainer,tkerola/chainer,niboshi/chainer,wkentaro/chainer,hvy/chainer,hvy/chainer,wkentaro/chainer,chainer/chainer,okuta/chainer