Bump postcss from 8.4.17 to 8.4.18 (#61)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.17 to 8.4.18.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.17...8.4.18)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -62,7 +62,7 @@
     "normalise": "^10.0.0",
     "normalize.css": "^8.0.1",
     "null-loader": "^4.0.1",
-    "postcss": "^8.4.17",
+    "postcss": "^8.4.18",
     "postcss-import": "^15.0.0",
     "postcss-loader": "^7.0.1",
     "postcss-preset-env": "^7.8.2",