chore: fix typings?

Author: imorland

extensions/realtime/js/src/@types/shims.d.ts

@@ -1,6 +1,5 @@
 import 'flarum/common/Application';
-import Pusher from 'pusher-js';
-import Channel from 'pusher-js';
+import Pusher, { Channel } from 'pusher-js';
 
 declare module 'flarum/common/Application' {
   export default interface Application {

extensions/realtime/js/src/forum/extend/Application.ts

@@ -1,10 +1,10 @@
 import { extend } from 'flarum/common/extend';
 import app from 'flarum/forum/app';
-import Pusher from 'pusher-js';
+import Pusher, { Channel } from 'pusher-js';
 import Application from 'flarum/common/Application';
 
 export default function () {
-  extend(Application.prototype, 'mount', function () {
+  extend(Application.prototype, 'mount' as any, function () {
     // Enable logging to console when debug is enabled.
     Pusher.logToConsole = this.forum.attribute<boolean>('debug');