Websockets 11 Support

[alanhdu]

Hi! right now, gql pins its websockets support to <11 -- do you know how much work it'd be to upgarde support for websockets 11? Judging from the changelog (https://websockets.readthedocs.io/en/stable/project/changelog.html#id7), it looks like the change should be quite manageable, especially since I don't think gql uses the sans-IO implementation (I might be wrong about that though!).

[leszekhanusz]

It should work fine.
All the tests are passing without any changes needed.

The modification was made in PR #424