Changed: apply htmlspecialchars_decode to [um_loggedin] output.

Issue: Issue with restrict content tags after version 2.0.54: html tags are not recognized at the lock text.
Link: https://secure.helpscout.net/conversation/917425392/32569?folderId=646527

includes/core/class-shortcodes.php

@@ -376,7 +376,7 @@ if ( ! class_exists( 'um\core\Shortcodes' ) ) {
 			}
 
 			$output = ob_get_clean();
-			return $output;
+			return htmlspecialchars_decode( $output );
 		}