message: ci_build: Upgrade the Python 'six' compatibility module
diff: @@ -31,8 +31,8 @@ pip2 install virtualenv
  pip3 install virtualenv
  # Install six.
  -pip2 install --upgrade six==1.10.0
  -pip3 install --upgrade six==1.10.0
  +pip2 install --upgrade six==1.11.0
  +pip3 install --upgrade six==1.11.0
  # Install absl-py.
  pip2 install --upgrade absl-py
  