fix(CouponCodeInput): mobile buttons adjusted

Related: quiqqer/template-cologne#103

src/QUI/ERP/Coupons/CodeGenerators/SimpleString.php

@@ -6,6 +6,7 @@
 
 namespace QUI\ERP\Coupons\CodeGenerators;
 
+use Exception;
 use QUI\ERP\Coupons\CodeGeneratorInterface;
 use QUI\ERP\Coupons\Handler;
 
@@ -27,9 +28,9 @@ class SimpleString implements CodeGeneratorInterface
      *
      * @param string $prefix (optional)
      * @return string
-     * @throws \Exception
+     * @throws Exception
      */
-    public static function generate($prefix = ''): string
+    public static function generate(string $prefix = ''): string
     {
         $characters = array_merge(
             range('A', 'Z'),