fixed the TF placeholder dimension mismatch in TF MNIST accuracy test
fixed the TF placeholder dimension mismatch in TF MNIST accuracy test

fartashf/cleverhans,openai/cleverhans,carlini/cleverhans,cihangxie/cleverhans,cleverhans-lab/cleverhans,carlini/cleverhans,cleverhans-lab/cleverhans,cleverhans-lab/cleverhans