Update requirements for TF 2.4.1
Update requirements for TF 2.4.1

TF 2.4.0 is crashing (illegal instruction) on a Ubuntu 20.04 installation that is up-to-date, and causing problems with pip installation for a release. This was required to finally fix TF, and is the most recent version.
deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel