Before

imports:
    - { resource: config.yml }

After

imports:
    - config.yml

Now the important question: should we update our examples? Should we use both formats? Only one of them? Which one? etc.

Personal comment: as I explained in symfony/symfony#23522 (comment) I think these changes create a lot of problems. Unless the new solution is 10 times better than the old solution, I don't think we should add alternative solutions to solve features.