Update primer.json to reflect Black's adoption (#1674)

- tox recently adopted Black  
https://github.com/tox-dev/tox/commit/a7903508fa07068b327e15cfdbf8ea330ab78765

- attrs already adopted Black but they updated to 20.08b1 + did a format pass and removed some trailing commas
https://github.com/python-attrs/attrs/commit/f680c5b83e65413eeb684c68ece60198015058c3