Switch to python 3.8 as default in CI and readme. (#686)
Summary:
After fixing a few compatibility issues, torchbenchmark can now run on both Python 3.7 and 3.8. We should switch to version 3.8 as default in the CircleCI and README.md.
This PR also moves to CUDA 11.3 as this is the CUDA version used in the nightly CI environment.
Pull Request resolved: https://github.com/pytorch/benchmark/pull/686
Reviewed By: robieta
Differential Revision: D33468193
Pulled By: xuzhao9
fbshipit-source-id: 7a60d18939eb8ee34ebef049d5c46f03a1ffb5a1
