message: add python protobuf package
diff: @@ -3,7 +3,7 @@ FROM envoyproxy/envoy:latest
  RUN apt-get update
  RUN apt-get -q install -y python-dev \
  python-pip
  -RUN pip install -q grpcio requests
  +RUN pip install -q grpcio protobuf requests
  ADD ./client /client
  RUN chmod a+x /client/client.py
  RUN mkdir /var/log/envoy/
  