TypeError: start_response() argument 1 must be str, not bytes

python 3.7+meinheld 1.0.2

bench/hello/meinheld_server.py:

```python
TypeError: start_response() argument 1 must be str, not bytes
Traceback (most recent call last):
  File "meinheld_server.py", line 7, in hello_world
    start_response(status, response_headers)
```