fix(index): fix demo page

Author: oterral

index.html

@@ -14,7 +14,7 @@
     <script src="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io/en/v6.4.3/build/ol.js"></script>
     <script src="https://unpkg.com/[email protected]/dist/mapbox-gl.js"></script>
     <script src="https://unpkg.com/[email protected]/dist/jsts.min.js"></script>
-    <script src="index.js"></script>
+    <script src="build/index.js"></script>
     <div id="app">
       <div id="header">
         <nav>