message: Use a virtualenv in uploading windows pips
  Seems that by default the version of `twine` that gets installed is too old
diff: @@ -18,16 +18,18 @@ set -x
  source tensorflow/tools/ci_build/release/common.sh
  -# TODO(mihaimaruseac): Convert all builds to start from a virtualenv to isolate
  -# from Kokoro setup
  -python3 -m pip install --upgrade --user twine
  +# Use a virtual environment to get access to the latest pips
  +python3 -m venv venv && source venv/bin/activate
  +
  +# Install a more recent version of twine
  +python -m pip install --upgrade 'twine >= 3.2.0'
  # Copy and rename to tf_nightly
  for f in $(ls "${KOKORO_GFILE_DIR}"/tf_nightly_gpu*dev*cp3*-cp3*-win_amd64.whl); do
  - copy_to_new_project_name "${f}" tf_nightly python3
  + copy_to_new_project_name "${f}" tf_nightly python
  done
  # Upload the built packages to pypi.
  for f in $(ls "${KOKORO_GFILE_DIR}"/tf_nightly*dev*cp3*-cp3*-win_amd64.whl); do
  - python3 -m twine upload -r pypi-warehouse "$f" || echo
  + python -m twine upload -r pypi-warehouse "$f" || echo
  done
  