Move to cabal-3.0

[chshersh]

This change implies:

• Changing defaultCabal
• Removing v2- prefixes
• Simplify cabal test (echo "No tests" no longer needed)
• Add --write-ghc-environment-files=always option

The following files need to be changed:

• .travis.yml
• Generated .travis.yml
• appveyor.yml
• Generated appveyor.yml
• .github/workflows/ci.yml
• Generated .github/workflows/ci.yml

[vrom911]

And changing cabal version in .cabal file and .travis.yml.

[srid]

Future: generated default.nix

Could you elaborate on what this means? I thought default.nix is hand-written?

[chshersh]

@srid The word generated in the context of this project means files and directories generated by summoner during his work. So ideally we are trying to use the same CI configs as summoner would generate during scaffolding. Dogfooding this project helps to improve UX 👍

After looking closely at default.nix again I don't see any cabal-related information in this package.... So we might not even need to change it at all if it uses cabal >= 3.0 by default.