Fix flake8 errors
Fix flake8 errors

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