message: Update install_pip_packages.sh
  Fixes a metaclass bug and adds __six.ensure_binary()__, __six.ensure_text()__, and
  __six.ensure_str()__.
diff: @@ -40,8 +40,8 @@ pip2 install virtualenv
  pip3 install virtualenv
  # Install six.
  -pip2 install --upgrade six==1.11.0
  -pip3 install --upgrade six==1.11.0
  +pip2 install --upgrade six==1.12.0
  +pip3 install --upgrade six==1.12.0
  # Install absl-py.
  pip2 install --upgrade absl-py
  