README: Fix broken Dockerhub repo link
README: Fix broken Dockerhub repo link

kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent,jaimeguzman/amazon-ecs-agent,aws/amazon-ecs-agent,seiffert/amazon-ecs-agent,seiffert/amazon-ecs-agent,swipely/amazon-ecs-agent,aws/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,aws/amazon-ecs-agent,swipely/amazon-ecs-agent,aws/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,jaimeguzman/amazon-ecs-agent