Change CDN from Unpkg to jsDelivr

jsDelivr supports CORP (https://resourcepolicy.fyi/#cross-origin) and
seems more robust.

Author: wangwillian0

web/index.html

@@ -27,8 +27,8 @@
   <link rel="apple-touch-icon" href="icons/Icon-192.png">
 
   <!-- Mapbox --> 
-  <script src='https://unpkg.com/mapbox-gl@latest/dist/mapbox-gl.js'></script>
-  <link href='https://unpkg.com/mapbox-gl@latest/dist/mapbox-gl.css' rel='stylesheet' />
+  <script src='https://cdn.jsdelivr.net/npm/mapbox-gl/dist/mapbox-gl.min.js'></script>
+  <link href='https://cdn.jsdelivr.net/npm/mapbox-gl/dist/mapbox-gl.min.css' rel='stylesheet' />
 
   <title>OpenHaystack Mobile</title>
   <link rel="manifest" href="manifest.json">