PadMessageHandler: Run the `userLeave` hook asynchronously

doc/api/hooks_server-side.md

@@ -834,7 +834,7 @@ Context properties:
 Example:
 
 ```javascript
-exports.userLeave = (hookName, {author, padId}) => {
+exports.userLeave = async (hookName, {author, padId}) => {
   console.log(`${author} left pad ${padId}`);
 };
 ```

src/node/handler/PadMessageHandler.js

@@ -148,7 +148,7 @@ exports.handleDisconnect = async (socket) => {
       },
     },
   });
-  hooks.callAll('userLeave', session);
+  await hooks.aCallAll('userLeave', session);
 };
 
 /**