missing compatibility with h11 0.13.0

[dirkmueller]

building against newer h11 releases gives these test failures:

[   33s] =================================== FAILURES ===================================
[   33s] ________________________________ test_handshake ________________________________
[   33s] 
[   33s]     def test_handshake() -> None:
[   33s]         response, nonce = _make_handshake([])
[   33s]     
[   33s] >       response.headers = sorted(response.headers)  # For test determinism
[   33s] 
[   33s] test/test_server.py:208: 
[   33s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[   33s] 
[   33s] self = InformationalResponse(headers=<Headers([(b'upgrade', b'WebSocket'), (b'connection', b'Upgrade'), (b'sec-websocket-accept', b'h8YJtSXCJagtWfHvVj0GxvhYXrM=')])>, http_version=b'1.1', reason=b'', status_code=101)
[   33s] name = 'headers'
[   33s] value = [(b'connection', b'Upgrade'), (b'sec-websocket-accept', b'h8YJtSXCJagtWfHvVj0GxvhYXrM='), (b'upgrade', b'WebSocket')]
[   33s] 
[   33s] >   ???
[   33s] E   dataclasses.FrozenInstanceError: cannot assign to field 'headers'
[   33s] 
[   33s] <string>:4: FrozenInstanceError
[   33s] _________________________ test_handshake_extra_headers _________________________
[   33s] 
[   33s]     def test_handshake_extra_headers() -> None:
[   33s]         response, nonce = _make_handshake([], accept_headers=[(b"X-Foo", b"bar")])
[   33s]     
[   33s] >       response.headers = sorted(response.headers)  # For test determinism
[   33s] 
[   33s] test/test_server.py:222: 
[   33s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[   33s] 
[   33s] self = InformationalResponse(headers=<Headers([(b'upgrade', b'WebSocket'), (b'connection', b'Upgrade'), (b'sec-websocket-accept', b'sbk5BhBG0603A9oxAGV4giGOq9k='), (b'x-foo', b'bar')])>, http_version=b'1.1', reason=b'', status_code=101)
[   33s] name = 'headers'
[   33s] value = [(b'connection', b'Upgrade'), (b'sec-websocket-accept', b'sbk5BhBG0603A9oxAGV4giGOq9k='), (b'upgrade', b'WebSocket'), (b'x-foo', b'bar')]
[   33s] 
[   33s] >   ???
[   33s] E   dataclasses.FrozenInstanceError: cannot assign to field 'headers'
[   33s] 
[   33s] <string>:4: FrozenInstanceError

[Kriechi]

@pgjones thoughts on how to best address this?

[pgjones]

I think so, I'll take a look this weekend.

[pgjones]

See #170