Update to the latest sage in preparation for live doc

[kwankyu]

I am rebooting sage live doc efforts

sagemath/sage#36144

[kwankyu]

Could updating sage here be automated?

Every push on develop (or master?) branch in sagemath/sage could trigger bumping up sage version here? @tobiasdiez @nthiery ?

[kwankyu]

As sage conda recipe is updated (now to sage 10.0), upgrading would be automatic here if - sage=9.6 is rewritten to - sage in https://github.com/sagemath/sage-binder-env/blob/master/environment.yml, I guess.

[kwankyu]

May I attain the maintainer role for this repo?

[kwankyu]

I am preparing a renewed binder repo at https://github.com/kwankyu/sage-binder-env, using Dockerfile.

This is for sagemath/sage#36144