(bug 44846) JSHint is always wrong in MediaWiki REL1_19

The Javascript linting fix have not been made in REL1_19 branch so we
want to skip the mediawiki-core-jslint for that branch. This use a regex
trick to trigger the job only when the branch does not match 'REL1_19'.

Change-Id: Ie9e18e669e254a0e8d73c04e641700fb76fc2f8b