include content-length to error response

src/server/error.rs

@@ -21,6 +21,7 @@ impl HttpHandlerTask for ServerError {
             bytes.reserve(helpers::STATUS_LINE_BUF_SIZE + 1);
             helpers::write_status_line(self.0, self.1.as_u16(), bytes);
         }
+        io.buffer().extend_from_slice(b"\r\ncontent-length: 0\r\n");
         io.set_date();
         Ok(Async::Ready(true))
     }