Replace deprecated String.prototype.substr()

.substr() is deprecated so we replace it with .slice() which works similarily but isn't deprecated

Signed-off-by: Tobias Speicher <rootcommander@gmail.com>

src/init-talk.js

@@ -46,7 +46,7 @@ window.addEventListener('DOMContentLoaded', () => {
 		icon: 'icon-deck',
 		async callback({ message: { message, actorDisplayName }, metadata: { name: conversationName, token: conversationToken } }) {
 			const shortenedMessageCandidate = message.replace(/^(.{255}[^\s]*).*/, '$1')
-			const shortenedMessage = shortenedMessageCandidate === '' ? message.substr(0, 255) : shortenedMessageCandidate
+			const shortenedMessage = shortenedMessageCandidate === '' ? message.slice(0, 255) : shortenedMessageCandidate
 			try {
 				await buildSelector(CardCreateDialog, {
 					props: {