updated project linter-rules and enforced them

lib/api/webuntis/queries/getHolidays/getHolidays.dart

@@ -4,7 +4,7 @@ import '../../webuntisApi.dart';
 import 'getHolidaysResponse.dart';
 
 class GetHolidays extends WebuntisApi {
-  GetHolidays() : super("getHolidays", null);
+  GetHolidays() : super('getHolidays', null);
 
   @override
   Future<GetHolidaysResponse> run() async {

lib/api/webuntis/queries/getHolidays/getHolidaysCache.dart

@@ -6,7 +6,7 @@ import 'getHolidaysResponse.dart';
 
 class GetHolidaysCache extends RequestCache<GetHolidaysResponse> {
   GetHolidaysCache({onUpdate}) : super(RequestCache.cacheDay, onUpdate) {
-    start("MarianumMobile", "wu-holidays");
+    start('MarianumMobile', 'wu-holidays');
   }
 
   @override