fix method name

Author: ardabeyazoglu

src/PhpWord/Element/CheckBox.php

@@ -82,6 +82,7 @@ public function getName()
     /**
      * set default checked status
      * @param bool $default
+     * @return CheckBox
      */
     public function setDefault(bool $default = false)
     {
@@ -93,7 +94,7 @@ public function setDefault(bool $default = false)
      * get default checked status
      * @return bool
      */
-    public function getDefault(): bool
+    public function isDefault(): bool
     {
         return $this->default;
     }