fix: array-form replacer should not filter Array elements

[spokodev]

stringify(value, replacer) with an array-form replacer diverges from native JSON.stringify. Per the spec, an allow-list replacer array filters only plain-object properties — array elements are always serialized regardless of index. flatted filters both, so array elements whose index isn't in the list are silently dropped, and the loss survives a parse(stringify(...)) round-trip:

JSON.stringify(['a', 'b', 'c'], ['0'])                    // '["a","b","c"]'  — all kept
Flatted.parse(Flatted.stringify(['a', 'b', 'c'], ['0']))  // ['a', null, null] — 2 lost

The wrapper was an arrow function, so it could not see the holder (this) that $.call(this, ...) passes it. Switching to a normal function and exempting array holders (Array.isArray(this)) matches native semantics. cjs/index.js is regenerated via npm run cjs.