Minor compatibility fix 2.1 - PLEASE create a release to have matchin…

…g version numbers for the released atk4/ui 2.2. Thank you (#10)

Co-authored-by: Michael Krecek <krecek@dte-systems.de>

src/Chart.php

@@ -60,7 +60,7 @@ public function init(): void
     /**
      * Renders chart view.
      */
-    public function renderView()
+    public function renderView(): void
     {
         $this->js(true, new jsExpression('new Chart([], []);', [$this->name, $this->getConfig()]));