Replace pytorch version provided by google colab with the one supporting TPU

pytorch-tpu-colab-setup.sh

TORCH_VER="20191208"
pip uninstall -y torch torchvision
rm -r wheels
mkdir -p wheels
for f in {torch,torch_xla,torchvision}; do 
  whl="${f}-nightly+${TORCH_VER}-cp36-cp36m-linux_x86_64.whl";
  gsutil cp "gs://tpu-pytorch/wheels/${whl}" wheels/;
  pip install "wheels/${whl}";
done
apt-get install -y libomp5
curl -vvv -d '{}' "http://$(echo $COLAB_TPU_ADDR | sed -Ee 's;[0-9]+$;8475;')/requestversion/XRT-dev${TORCH_VER}"