Bump postcss from 7.0.24 to 8.2.1

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.24 to 8.2.1.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.24...8.2.1)

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

Author: dependabot-preview[bot]

package.json

@@ -69,7 +69,7 @@
         "less-loader": "^7.0.1",
         "mini-css-extract-plugin": "^1.3.3",
         "pixelmatch": "^4.0.2",
-        "postcss": "^7.0.0",
+        "postcss": "^8.2.1",
         "postcss-loader": "^4.1.0",
         "react-hot-loader": "^4.7.1",
         "react-test-renderer": "^16.12.0",