Bump postcss from 8.2.15 to 8.3.0

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.15 to 8.3.0.
- [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/8.2.15...8.3.0)

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

package.json

@@ -31,7 +31,7 @@
     "@types/react-calendar": "^3.1.6",
     "@types/uuid": "^8.3.0",
     "jest": "^26.6.3",
-    "postcss": "^8.2.15",
+    "postcss": "^8.3.0",
     "postcss-flexbugs-fixes": "^5.0.2",
     "postcss-preset-env": "^6.7.0",
     "swr": "^0.5.6",