build(deps): bump rollup-plugin-postcss from 2.5.0 to 3.1.1

Bumps [rollup-plugin-postcss](https://github.com/egoist/rollup-plugin-postcss) from 2.5.0 to 3.1.1.
- [Release notes](https://github.com/egoist/rollup-plugin-postcss/releases)
- [Changelog](https://github.com/egoist/rollup-plugin-postcss/blob/master/CHANGELOG-OLD.md)
- [Commits](https://github.com/egoist/rollup-plugin-postcss/compare/v2.5.0...v3.1.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

packages/cli/package.json

@@ -59,7 +59,7 @@
     "rollup": "^2.3.2",
     "rollup-plugin-image-files": "^1.4.2",
     "rollup-plugin-peer-deps-external": "^2.2.2",
-    "rollup-plugin-postcss": "^2.5.0",
+    "rollup-plugin-postcss": "^3.1.1",
     "rollup-plugin-typescript2": "^0.26.0",
     "tar": "^6.0.1",
     "ts-loader": "^7.0.4",