Update deprecated usage of asyncio.wait() (#281)

Author: musicinmybrain

src/engineio/asyncio_server.py

@@ -175,7 +175,7 @@ async def disconnect(self, sid=None):
                 if sid in self.sockets:  # pragma: no cover
                     del self.sockets[sid]
         else:
-            await asyncio.wait([client.close()
+            await asyncio.wait([asyncio.create_task(client.close())
                                 for client in self.sockets.values()])
             self.sockets = {}