fix contribution guide for test framework change
fix contribution guide for test framework change

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