Update app.json

For Heroku, add the Tor buildpack to allow for Tor connections.

app.json

@@ -20,7 +20,8 @@
   },
   "buildpacks": [
     {
-      "url": "https://github.com/heroku/heroku-buildpack-go"
+      "url": "https://github.com/heroku/heroku-buildpack-go",
+      "url": "https://github.com/iamashks/heroku-buildpack-tor-proxy.git"
     }
   ]
-}
+}