message: Use debian:stretch-slim for freebindfree builds
diff: # Freebind build
  -FROM node:12-slim as freebind
  +# node:12-slim uses debian:stretch-slim as a base, so it's safe to build on here.
  +FROM debian:stretch-slim as freebind
  RUN apt-get update \
  && apt-get install -y git build-essential
  