[v11.3.x] Fix param to setPresence in setActivity (#2270)

ClientUser#setPresence in master branch (latest) calls client.presences.setClientPresence, but that in v11.3 does not
so i change parameter sent to setPresence for clearing the game activity, from activity:null to game:null,
for now until setPresence gets updated

src/structures/ClientUser.js

@@ -271,7 +271,7 @@ class ClientUser extends User {
    * @returns {Promise<Presence>}
    */
   setActivity(name, { url, type } = {}) {
-    if (!name) return this.setPresence({ activity: null });
+    if (!name) return this.setPresence({ game: null });
     return this.setPresence({
       game: { name, type, url },
     });