[IDC-2052] PWA start url (#2070)

Change start_url in manifest.json from "./index.html" to "./"

Co-authored-by: Woonchan Cho <wcho24@wustl.edu>

platform/viewer/public/manifest.json

@@ -52,7 +52,7 @@
       "type": "image/png"
     }
   ],
-  "start_url": "./index.html",
+  "start_url": "./",
   "background_color": "#000000",
   "display": "standalone",
   "theme_color": "#20a5d6"