Fix the Jenkins Docker Permission denied when trying to connect to Docker daemon socket error

There's an easy fix to the Jenkins Docker permission error that spits something like this out in the console of your Jenkins build jobs: Got permission denied while trying to connect to the Docker daemon socket at docker.sock: Get containers/maven:3.3.3/json: dial unix docker.sock: connect: permission denied. Just run: 'sudo usermod -a -G docker jenkins' in the Ubuntu Linux terminal and then reboot.