fixes docker publish workflow

It looks like that the newest version of z3 doesn't build on the older
ubuntu distributions. We can try constraining them to the latest
version that was providing the static version.

Author: ivg

docker/ubuntu/bionic/Dockerfile

@@ -10,7 +10,7 @@ RUN sudo apt-get update  \
  && opam remote set-url default https://opam.ocaml.org \
  && opam repo add bap git+https://github.com/BinaryAnalysisPlatform/opam-repository --all \
  && opam update \
- && opam depext --install bap-extra --yes -j 1 \
+ && opam depext --install bap-extra "z3=4.8.11" --yes -j 1 \
  && opam clean -acrs
 
 ENTRYPOINT ["opam", "config", "exec", "--"]