Add missing public-url to parcel build

Author: Ari-Matti Nivasalo

package.json

@@ -5,7 +5,7 @@
   "main": "index.js",
   "scripts": {
     "dev": "parcel index.html --open",
-    "build": "parcel build index.html",
+    "build": "parcel build index.html --public-url /assets",
     "postinstall": "npm run build",
     "test": "jest"
   },