Update nix to nix 2.13

[cidkidnix]

Obelisk is currently using an old version of nix for ob commands, this updates nix to get us on a newer version.

Notable changes:

• nix eval has changed due to the new nix commands, added --impure and --expr to make them function the same again

I have:

• Based work on latest develop branch
• Followed the contribution guide
• Looked for lint in my changes with hlint . (lint found code you did not write can be left alone)
• [] Run the test suite: $(nix-build -A selftest --no-out-link)
• Updated the changelog
• (Optional) Run CI tests locally: nix-build release.nix -A build.x86_64-linux --no-out-link (or x86_64-darwin on macOS)

[ali-abrar]

Any reason not to proceed with this @cidkidnix