Make ErrorSpec take a (NonEmpty String) rather than [String]

[TimSheard]

All too often, when running a test, the test fails, and the explanation of the failure is the empty list ([]) of explanations.
Try as hard as I could, I could never trackdown where this list was coming from.

One of the design goals of the constrained generators was that failures should be explained.
So under the better design goal, that every failure should have a non-empty explanation, I have changed the
type of ErrorSpec from
ErrorSpec :: [String] -> Specification fn a
ErrorSpec :: Data.List.NonEmpty String -> Specification fn a

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[teodanciu]

It looks like in base for 8.10.7 there is no singleton and append exported from Data.List.NonEmpty , so I think you might need to replace these with the constructor :| and <>, respectively, on order to make the PR compile for 8.10.7.

[teodanciu]

Looks good to me but I think you need to change the singleton and append from NonEmpty in order to be able to merge it.