ci: Make run-eslint more convenient for local use

ci: Make run-eslint more convenient for local use

The script can be helpful outside of CI, in particular for gradually
transitioning to the new style.

Reverting commit f00201fa6ca it is already possible to do something
like

 $ CI_MERGE_REQUEST_PROJECT_URL=https://gitlab.gnome.org/GNOME/gnome-shell \
   CI_MERGE_REQUEST_TARGET_BRANCH_NAME=master CI_COMMIT_SHA=HEAD \
   .gitlab-ci/run-eslint.sh

but that is hardly convenient.

Instead, allow passing the required parameters on the command line:

 $ .gitlab-ci/run-eslint.sh origin master

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/730