Use same method to obtain the avatar image in testWebhook and streamUpdate

app/Http/Controllers/WebhookController.php

@@ -86,7 +86,7 @@ class WebhookController extends Controller
         $message = new DiscordTextMessage();
         $message->setContent("Test message.")
             ->setUsername(config("app.name"))
-            ->setAvatar(config("app.url") . "/img/twitch-icon.png");
+            ->setAvatar(asset("img/twitch-icon.png"));
 
         $webhook = new DiscordWebhook($request->discord_hook_url);
         $webhook->send($message);