remove unnecessary default

src/structures/Chat.js

@@ -150,7 +150,7 @@ class Chat extends Base {
      * Mutes this chat forever, unless a date is specified
      * @param {?Date} unmuteDate Date at which the Chat will be unmuted, leave as is to mute forever
      */
-    async mute(unmuteDate = undefined) {
+    async mute(unmuteDate) {
         return this.client.muteChat(this.id._serialized, unmuteDate);
     }