`@types/stylelint` is deprecated

[skjnldsv]

While investigating CVE-2021-23382, I could not update postcss because I'm using this plugin which is using @types/stylelint

├─┬ stylelint-webpack-plugin@3.1.0
│ └─┬ @types/stylelint@13.13.3
│   └── postcss@7.0.39

@types/stylelint has released a new version, and is statingyou should not use that package anymore
https://www.npmjs.com/package/@types/stylelint

[skjnldsv]

Fix in #254