dockerfile: edit timezone for Shanghai timezone

Dockerfile

@@ -23,7 +23,7 @@ owner="yiping.xu"
 WORKDIR /app/kpt-tmr
 
 RUN apk add --no-cache tzdata \
-&& cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime \
+&& ln -sv /usr/share/zoneinfo/Asia/Shanghai /etc/localtime \
 && echo "Asia/Shanghai" > /etc/timezone \
 && apk del tzdata