make cuDNN version more unambiguous
make cuDNN version more unambiguous

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