message: Update TFLM to use python:3.9-buster.
diff: # Use a prebuilt Python image instead of base Ubuntu to speed up the build process,
  # since it has all the build dependencies we need for Micro and downloads much faster
  # than the install process.
  -FROM python:3.5-stretch
  +FROM python:3.9.0-buster
  LABEL maintainer="Pete Warden <petewarden@google.com>"
  