[fix] destroy() websockets in case of an error

Not doing so caused websockets in `CLOSE_WAIT` to pile up and cause
proxy to exceed open file descriptor limit.

Author: mmalecki

lib/node-http-proxy/http-proxy.js

@@ -611,12 +611,17 @@ HttpProxy.prototype.proxyWebSocketRequest = function (req, socket, head, buffer)
   // connections.
   //
   function proxyError (err) {
-    reverseProxy.end();
-    if (self.emit('webSocketProxyError', req, socket, head)) {
-      return;
-    }
+    reverseProxy.destroy();
+
+    process.nextTick(function () {
+      //
+      // Destroy the incoming socket in the next tick, in case the error handler
+      // wants to write to it.
+      //
+      socket.destroy();
+    });
 
-    socket.end();
+    self.emit('webSocketProxyError', req, socket, head);
   }
 
   //