Small fix for Epoll version of Async (uNetworking#753)

* In Epoll version of Async::close(), delete itself as Async* instead of Poll*

* Star to the right

src/Epoll.h

@@ -243,7 +243,7 @@ struct Async : Poll {
  Poll::stop(loop);
  ::close(state.fd);
  Poll::close(loop, [](Poll *p) {
- delete p;
+ delete (Async *) p;
  });
  }