run the yarn-installed grunt version instead of relying on local grunt

(attempt to fix stuff #1 (closed))

cc @laurent.heirendt

added 16 commits

• f8055b17...4338c2c7 - 15 commits from branch master
• 6a5f2ad4 - run the yarn-installed grunt version instead of relying on local grunt

Compare with previous version

merged

mentioned in commit be9a96de