Fixed: load stepper in backend

src/Stepper.php

@@ -40,7 +40,7 @@ class Stepper {
     }
 
     public function handle() {
-        echo $this->twig->render('stepper.twig.htm', [
+        return $this->twig->render('stepper.twig.htm', [
             'sprite' => $this->url.'assets/public/sprite.svg'
         ]);
     }

stepper.php

@@ -17,7 +17,9 @@ require_once(__DIR__.'/vendor/autoload.php');
 use Zoomyboy\Stepper\Stepper;
 
 
-$stepper = new Stepper();
-$stepper->url = plugin_dir_url(__FILE__);
-$stepper->init();
+if (!is_admin()) {
+    $stepper = new Stepper();
+    $stepper->url = plugin_dir_url(__FILE__);
+    $stepper->init();
+}