[BUGFIX] define rendertype for php versions

Configuration/TCA/tx_typo3roadmap_domain_model_majorversion.php

@@ -150,6 +150,7 @@ return array(
             'label'   => 'LLL:EXT:typo3_roadmap/Resources/Private/Language/locallang_db.xml:tx_typo3roadmap_domain_model_majorversion.php_versions',
             'config'  => array(
                 'type'                => 'select',
+                'renderType'          => 'selectCheckBox',
                 'foreign_table'       => 'tx_typo3roadmap_domain_model_phpversion',
                 'foreign_table_where' => 'ORDER BY tx_typo3roadmap_domain_model_phpversion.uid',
                 'size'                => 10,