apply method
Apply method, return the generated string
Implementation
@override
String apply() {
final numDigits = Random().nextDouble() > 0.5 ? 1 : 2;
return '${_postcodes[Random().nextInt(_postcodes.length - 1)]}'
'${DartamakerPluginDigits(numDigits.toString()).apply()} '
'${DartamakerPluginDigits('1').apply()}'
'${DartamakerPluginLetters('2').apply()}';
}