Moodle – Upgrade version with Git from 3.3-3.*

First Step: 

 git remote add upstream https://github.com/moodle/moodle.git

Second Step: 

vim update.sh 
#!/bin/bash
git fetch upstream
for BRANCH in MOODLE_{31..37}_STABLE master;
do
git push origin refs/remotes/upstream/$BRANCH:refs/heads/$BRANCH
done

Source: https://docs.moodle.org/dev/Git_for_developers