Convert `ember-cli-babel` to dev dependency
Convert `ember-cli-babel` to dev dependency

`ember-cli-babel` does not seem to be used by this addon as the `app` and `addon` folders are essentially empty. This will allow users of this addon to drop `ember-cli-shims` as that requires that all used addons use at least v6.6.0 of `ember-cli-babel`.

billybonks/ember-cli-stylelint,billybonks/ember-cli-stylelint