Motivation for this change

Upgrade to the first official release: https://github.com/microsoft/debugpy/releases/tag/v1.0.0

Also fixes the Python 2.7 build

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)

• Built on platform(s)

  • NixOS
  • macOS
  • other Linux distributions

• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)

• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"

  $ nix-env -f /home/kira/.cache/nixpkgs-review/rev-7539c63103c14fe3ed5da473fa26988d71b51450/nixpkgs -qaP --xml --out-path --show-trace --meta
  1 package added:
  python27Packages.debugpy (init at 1.0.0)
  
  2 packages updated:
  python37Packages.debugpy (1.0.0b12 → 1.0.0) python38Packages.debugpy (1.0.0b12 → 1.0.0)
  
  $ nix build --no-link --keep-going --option build-use-sandbox relaxed -f /home/kira/.cache/nixpkgs-review/rev-7539c63103c14fe3ed5da473fa26988d71b51450/build.nix
  3 packages built:
  python27Packages.debugpy python37Packages.debugpy python38Packages.debugpy
  

• Tested execution of all binary files (usually in ./result/bin/)
  No bin files, only a python library. Tested through dap-mode in Emacs.

• Determined the impact on package closure size (by running nix path-info -S before and after)

• Ensured that relevant documentation is up to date

• Fits CONTRIBUTING.md.