fix(typings): do not expose browser-specific types

Related:

- #1561
- b862924
- socketio/engine.io-client@37d7a0a

Author: darrachequesne

lib/socket.ts

@@ -102,7 +102,7 @@ export type DisconnectDescription =
   | Error
   | {
       description: string;
-      context?: CloseEvent | XMLHttpRequest;
+      context?: unknown; // context should be typed as CloseEvent | XMLHttpRequest, but these types are not available on non-browser platforms
     };
 
 interface SocketReservedEvents {