gitlab-ci: Use env bash as interpreter
bash is installed i /bin in all the systems, while it's uncommon to be in /usr/bin, causing this error when running the scripts locally:
bash: .gitlab-ci/run-eslint.sh: /usr/bin/bash: bad interpreter: No such file or directory
Set the shabang to point to the /bin version to make this work everywhere.
Edited by Marco Trevisan