dev: update NPM scripts

Author: uwla

package.json

@@ -9,7 +9,7 @@
         "build:ts": "vue-tsc && mv dist/main.d.ts vue-form-builder.d.ts",
         "build:js": "vite build && mv vue-form-builder.d.ts dist/",
         "build": "npm run build:ts && npm run build:js",
-        "build:demo": "vite build --config vite.config.dev.ts",
+        "build:demo": "APP_BASE=/demo vite build --config vite.config.dev.ts",
         "dev": "vite --config vite.config.dev.ts",
         "test": "vitest run"
     },