chore(dev-mashup): Fix broken yarn start (#893)

* chore: adaptations to parcel v.2

examples/dev-mashup/index.html

@@ -53,6 +53,6 @@
       <div class="listbox"></div>
     </div>
 
-    <script src="index.js"></script>
+    <script type="module" src="index.js"></script>
   </body>
 </html>

examples/dev-mashup/package.json

@@ -2,7 +2,7 @@
   "name": "local-mashup",
   "version": "1.0.0",
   "description": "Simple local mashup",
-  "main": "index.html",
+  "main": "index.js",
   "scripts": {
     "start": "parcel index.html --open --no-hmr",
     "build": "parcel build index.html"