Fix flake8 errors
Fix flake8 errors

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