Bump postcss from 8.2.14 to 8.2.15

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.14 to 8.2.15.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.2.14...8.2.15)

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

package.json

@@ -60,7 +60,7 @@
     "jest": "^26.6.3",
     "mini-css-extract-plugin": "^1.6.0",
     "optimize-css-assets-webpack-plugin": "^5.0.4",
-    "postcss": "^8.2.14",
+    "postcss": "^8.2.15",
     "postcss-loader": "^5.2.0",
     "prettier": "^2.3.0",
     "prettier-webpack-plugin": "^1.2.0",