build: ⬆️ bump postcss from 8.2.14 to 8.2.15 in /docs

Author: luthfimasruri

docs/package-lock.json

@@ -14,7 +14,7 @@
   "devDependencies": {
     "autoprefixer": "^10.2.5",
     "cross-env": "^7.0.3",
-    "postcss": "^8.2.14",
+    "postcss": "^8.2.15",
     "tailwindcss": "^2.1.2",
     "types-quill-delta": "^1.0.0",
     "vitepress": "^0.13.2"