Fix following from Preroma does not complete (#2905)

* In Follow Accept/Reject, send previous received id

* In Follow Accept/Reject, send Activity.actor

src/remote/activitypub/renderer/reject.ts

@@ -1,4 +1,8 @@
-export default (object: any) => ({
+import config from '../../../config';
+import { ILocalUser } from '../../../models/user';
+
+export default (object: any, user: ILocalUser) => ({
 	type: 'Reject',
+	actor: `${config.url}/users/${user._id}`,
 	object
 });