Use mgr:info as healtcheck

Dockerfile

@@ -104,7 +104,7 @@ RUN adduser --no-create-home --uid 1161 --group --system squid \
     && rm -rf /var/lib/apt/lists/* && rm -Rf /tmp/* 
 COPY run.sh /
 RUN chmod +x /run.sh
-HEALTHCHECK CMD squidclient mgr:index | grep "HTTP/1.1 200 OK" || exit 1
+HEALTHCHECK CMD squidclient mgr:info | grep "HTTP/1.1 200 OK" || exit 1
 EXPOSE 3128
 ENTRYPOINT ["dumb-init"]
 CMD ["bash", "-c", "/run.sh && squid -N -n $HOSTNAME"]