Oh, I discovered that It was easier than what Marcus sugested
the env variables MIX_BUILD_ROOT and MIX_DEPS_PATH overrides build_path and deps_path, so you just have to add
environment:
MIX_BUILD_ROOT: /opt/elixir-artifacts/_build
MIX_DEPS_PATH: /opt/elixir-artifacts/deps
volumes:
- elixir-artifacts:/opt/elixir-artifacts
to your docker-compose 
