update depcrecated image, fix minor Label change
update depcrecated image, fix minor Label change

Java is deprecated as the state:
"This image is officially deprecated in favor of the openjdk image, and will receive no further updates after 2016-12-31 (Dec 31, 2016). Please adjust your usage accordingly."

I adjusted it to the corresponding 7-alpine-jre tag  from openjdk
https://hub.docker.com/_/openjdk/

the MAINTAINER instruction is deprecated as of Docker Version: 
1.13.0
https://docs.docker.com/engine/deprecated/#maintainer-in-dockerfile

all the best
andrewgaul/s3proxy,timuralp/s3proxy,andrewgaul/s3proxy,timuralp/s3proxy