Refactor: Apply Rabbit Suggestion to InstantJsonAdapter

// 3 option: replace Instant by another class, use a third party library to make retrocompatibility

// or update android minimum api to at least API 26

class InstantJsonAdapter {

    companion object {

        private val FORMATTER: DateTimeFormatter = DateTimeFormatter.ISO_INSTANT

    }

    @ToJson

    fun toJson(instant: Instant): String {

        return DateTimeFormatter.ISO_INSTANT.format(instant)

        return FORMATTER.format(instant)

    }

    @FromJson