resolve docker build warnings

Author: ChenHuajun

docker-example/Dockerfile

@@ -1,6 +1,7 @@
 FROM postgres:16.0-bookworm AS builder
-ENV VERSION_TAG 0.5.4
+ENV VERSION_TAG=0.5.4
 
+WORKDIR /
 RUN apt-get update && apt-get install -y curl unzip make gcc postgresql-server-dev-16
 RUN curl -LO "https://github.com/ChenHuajun/pg_roaringbitmap/archive/refs/tags/v$VERSION_TAG.zip"
 RUN unzip "v$VERSION_TAG.zip"

docker-example/docker-compose.yml

@@ -1,5 +1,3 @@
-version: '3.8'
-
 services:
     database:
       build: