AsyncSocketMiddleware: Fix synchronization on the wrong object.

Fixes: koush#53

Author: koush

AndroidAsync/src/com/koushikdutta/async/http/AsyncSocketMiddleware.java

@@ -236,7 +236,7 @@ private void recycleSocket(final AsyncSocket socket, AsyncHttpRequest request) {
             socket.setClosedCallback(new CompletedCallback() {
                 @Override
                 public void onCompleted(Exception ex) {
-                    synchronized (this) {
+                    synchronized (AsyncSocketMiddleware.this) {
                         ss.remove(socket);
                     }
                     socket.setClosedCallback(null);