Use __struct__ in place of __record__(:name)

Fixes the below failure
```
1) test ! negates the predicate - raises (Integration.AmritaFacts)
     test/integration/t_amrita.exs:317
     ** (ArgumentError) argument error
     stacktrace:
       (amrita) lib/amrita/checkers/simple.ex:223: Amrita.Checkers.Simple.!/2
       test/integration/t_amrita.exs:318
```