Fix flake8 violation
Fix flake8 violation

wkentaro/chainer,kiyukuta/chainer,kashif/chainer,hvy/chainer,okuta/chainer,ysekky/chainer,hvy/chainer,chainer/chainer,jnishi/chainer,ktnyt/chainer,chainer/chainer,wkentaro/chainer,rezoo/chainer,keisuke-umezawa/chainer,jnishi/chainer,ktnyt/chainer,niboshi/chainer,ktnyt/chainer,hvy/chainer,niboshi/chainer,keisuke-umezawa/chainer,ktnyt/chainer,aonotas/chainer,okuta/chainer,jnishi/chainer,chainer/chainer,jnishi/chainer,keisuke-umezawa/chainer,hvy/chainer,wkentaro/chainer,pfnet/chainer,chainer/chainer,okuta/chainer,keisuke-umezawa/chainer,tkerola/chainer,wkentaro/chainer,anaruse/chainer,niboshi/chainer,delta2323/chainer,niboshi/chainer,okuta/chainer,ronekko/chainer