fix: upgrade postcss from 8.4.5 to 8.4.6

Snyk has created this PR to upgrade postcss from 8.4.5 to 8.4.6.

See this package in npm:
https://www.npmjs.com/package/postcss

See this project in Snyk:
https://app.snyk.io/org/ytetsuro/project/5c9d5982-3265-4dba-90fc-6fc790ca8257?utm_source=github&utm_medium=referral&page=upgrade-pr

package.json

@@ -20,7 +20,7 @@
     "mithril": "^2.0.4",
     "pako": "^1.0.11",
     "php-parser": "^3.0.3",
-    "postcss": "^8.4.5",
+    "postcss": "^8.4.6",
     "postcss-import": "^14.0.2",
     "reflect-metadata": "^0.1.13",
     "tslib": "^1.14.1",