Use ensure_resource insted of stdlib::ensure_packages

[deric]

This way stdlib >= 9 is not required (#77)

If I'm not mistaken ensure_packages calls under the hood ensure_resource. So the functionality should be the same.

This might relax dependencies of this module. Sorry, I'm a bit late with the PR 😞

Instead of jumping dependency from >=2.6.0 to 9.0.0 we might be able to use >=4.12.0 as minimal puppetlabs/stdlib requirement.