using UK time instead of german time for requests

lib/services/api.dart

@@ -1,5 +1,6 @@
 import 'package:http/http.dart' as http;
 import 'dart:convert';
+import 'package:timezone/timezone.dart' as tz;
 
 import '../model/flood_station.dart';
 import '../model/reading.dart';
@@ -40,9 +41,9 @@ class Api {
   static Future<List<Reading>> fetchReadingsFromStation(
       String stationId) async {
     List<Reading> readings = [];
-    final dateTime = DateTime.now().subtract(Duration(days: 1));
+    final dateTime = _getCurrentUKTime().subtract(Duration(days: 1)).toUtc();
     final url =
-        '$_rootUrl/id/stations/$stationId/readings?since=${dateTime.toIso8601String()}Z&_sorted';
+        '$_rootUrl/id/stations/$stationId/readings?since=${dateTime.toIso8601String()}&_sorted';
     final response = await http.get(Uri.parse(url));
     if (response.statusCode == 200) {
       final Map<String, dynamic> jsonStr = jsonDecode(response.body);
@@ -52,4 +53,9 @@ class Api {
     }
     return readings.reversed.toList();
   }
+
+  static DateTime _getCurrentUKTime() {
+    final london = tz.getLocation('Europe/London');
+    return tz.TZDateTime.now(london);
+  }
 }