fix: make closeOnBeforeunload default to false

Silently closing the connection when receiving a "beforeunload" event
is problematic, because it is emitted:

- when downloading a file from another host

Related: socketio/socket.io#4436

- when the user already has a listener for the "beforeunload" event
(i.e. "are you sure you want to leave this page?")

Related:

- #661
- #658
- socketio/socket.io#4065

That's why the `closeOnBeforeunload` option will now default to false.

lib/socket.ts

@@ -170,7 +170,7 @@ export interface SocketOptions {
 
   /**
    * Whether to automatically close the connection whenever the beforeunload event is received.
-   * @default true
+   * @default false
    */
   closeOnBeforeunload: boolean;
 
@@ -347,7 +347,7 @@ export class Socket extends Emitter<
           threshold: 1024,
         },
         transportOptions: {},
-        closeOnBeforeunload: true,
+        closeOnBeforeunload: false,
       },
       opts
     );