Update tf-nightly requirement to 2.3 (#151)
Update tf-nightly requirement to 2.3 (#151)

2.2 is no longer available.  Using compatible release clause `~=` will allow pip to find the latest 2.3 nightly

https://www.python.org/dev/peps/pep-0440/#compatible-release
keras-team/keras-io,keras-team/keras-io