Form::addGroup() loose type (#269)

Allow more types of $caption

Author: kotr7

src/Forms/Form.php

@@ -234,8 +234,9 @@ public function addProtection(string $errorMessage = null): Controls\CsrfProtect
 
 	/**
 	 * Adds fieldset group to the form.
+	 * @param string|object $caption
 	 */
-	public function addGroup(string $caption = null, bool $setAsCurrent = true): ControlGroup
+	public function addGroup($caption = null, bool $setAsCurrent = true): ControlGroup
 	{
 		$group = new ControlGroup;
 		$group->setOption('label', $caption);