Explicitly add prettier to dev deps

package.json

@@ -20,7 +20,8 @@
     "build:demo": "vite build --mode demo",
     "preview": "vite preview",
     "serve": "vite preview",
-    "test": "vitest"
+    "test": "vitest",
+    "format": "prettier ./lib ./demo  -w -u"
   },
   "dependencies": {},
   "devDependencies": {
@@ -36,6 +37,7 @@
     "highlight.js": "^11.4.0",
     "jsdom": "^19.0.0",
     "postcss": "^8.4.5",
+    "prettier": "^2.5.1",
     "tailwindcss": "^3.0.15",
     "tributejs": "^5.1.3",
     "typescript": "^4.4.4",