add zlib1g-dev to Dockerfile

Current Docker-based build fails without it

Dockerfile

@@ -8,6 +8,7 @@ RUN apt-get update && apt-get install -y \
     python3 \
     libjson-c-dev \
     git \
+    zlib1g-dev \
     && rm -rf /var/lib/apt/lists/*
 
 # git safe.directory for mounted repos (Makefile uses git describe)