message: [docker] fix cpu image after 0.23.0 release
diff: @@ -21,5 +21,6 @@ FROM python:${PYTHON_VERSION}
  # tfio package name and version for pip install
  ARG TFIO_PACKAGE=tensorflow-io
  ARG TFIO_PACKAGE_VERSION=
  +ARG TENSORFLOW_VARIANT=tensorflow
  -RUN pip install ${TFIO_PACKAGE}${TFIO_PACKAGE_VERSION:+==${TFIO_PACKAGE_VERSION}}
  +RUN pip install ${TFIO_PACKAGE}${TFIO_PACKAGE_VERSION:+==${TFIO_PACKAGE_VERSION}}[${TENSORFLOW_VARIANT}]
  