fixed a compiling error
fixed a compiling error

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