Updated CDN and $version in App.php to 1.5.3

Author: romaninsh

src/App.php

@@ -16,15 +16,15 @@ class App
 
     // @var array|false Location where to load JS/CSS files
     public $cdn = [
-        'atk'              => 'https://cdn.rawgit.com/atk4/ui/1.5.2/public',
+        'atk'              => 'https://cdn.rawgit.com/atk4/ui/1.5.3/public',
         'jquery'           => 'https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1',
         'serialize-object' => 'https://cdnjs.cloudflare.com/ajax/libs/jquery-serialize-object/2.5.0',
         'semantic-ui'      => 'https://cdnjs.cloudflare.com/ajax/libs/semantic-ui/2.3.1',
         'calendar'         => 'https://cdn.rawgit.com/mdehoog/Semantic-UI-Calendar/0.0.8/dist',
     ];
 
     // @var string Version of Agile UI
-    public $version = '1.5.2';
+    public $version = '1.5.3';
 
     // @var string Name of application
     public $title = 'Agile UI - Untitled Application';