clean-css 4.x dependencie

[kevin-loumont]

We will need to delete the resolution deps of clean-css when ember-cli will upgrade his deps to ember-cli-preprocess-registry v4.x.x because it doens't use it anymore

//package.json "resolutions": { "clean-css": "^4.1.11" }

it could also bring new issue with node.js 12
see: ember-cli/ember-cli-preprocess-registry#71

[MrChocolatine]

The resolution to [email protected] was removed in the pull request #126 (commit a6d6a25).

I am closing this issue.