chore: Add SPDX header

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

src/helpers/mentions.js

@@ -1,3 +1,7 @@
+/**
+ * SPDX-FileCopyrightText: 2020 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
 const rawToParsed = (text) => {
 	text = text.replace(/<br>/g, '\n')
 	text = text.replace(/&nbsp;/g, ' ')