Security: Update dependencies

[kevin-loumont]

close #8

Before update :

What i did: yarn upgrade

Result:

To fix the last vulnerabilitie i add :

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

Result:

[GreatWizard]

I'm not a big fan to update a major version of a dependencies in resolutions.
But it seems that upgrade from v3 to v4 don't change anything in the code in clean-css-promise, so it's all fine with the resolutions: shinnn/clean-css-promise@01a858f

---

Also, it seems that clean-css comes from https://github.com/shinnn/clean-css-promise/blob/master/package.json#L34 => https://github.com/shinnn/broccoli-clean-css/blob/master/package.json#L35 => https://github.com/ember-cli/ember-cli-preprocess-registry/blob/v3.3.0/package.json#L25 => https://github.com/ember-cli/ember-cli/blob/master/package.json#L76

If we look at the latest verison of ember-cli-preprocess-registry (https://github.com/ember-cli/ember-cli-preprocess-registry/blob/master/package.json) the deps on clean-css stuff is removed ;) So we will be able to remove that resolutions when ember-cli will upgrade the deps to ember-cli-preprocess-registry v4.x.x.