Add TextRun as container for CheckBox

Author: solovyovbdc

src/PhpWord/Element/AbstractContainer.php

@@ -207,7 +207,7 @@ private function checkValidity($method)
             'ListItem'      => array('Section', 'Header', 'Footer', 'Cell', 'TextBox'),
             'ListItemRun'   => array('Section', 'Header', 'Footer', 'Cell', 'TextBox'),
             'Table'         => array('Section', 'Header', 'Footer', 'Cell', 'TextBox'),
-            'CheckBox'      => array('Section', 'Header', 'Footer', 'Cell'),
+            'CheckBox'      => array('Section', 'Header', 'Footer', 'Cell', 'TextRun'),
             'TextBox'       => array('Section', 'Header', 'Footer', 'Cell'),
             'Footnote'      => array('Section', 'TextRun', 'Cell'),
             'Endnote'       => array('Section', 'TextRun', 'Cell'),