[SetPushRequest] make required field required in the class too

Took 6 minutes

lib/src/requests/SetPushersRequest.dart

@@ -21,6 +21,7 @@
  * along with famedly.  If not, see <http://www.gnu.org/licenses/>.
  */
 import 'package:json_annotation/json_annotation.dart';
+import 'package:meta/meta.dart';
 
 part 'SetPushersRequest.g.dart';
 
@@ -47,13 +48,13 @@ class SetPushersRequest {
   bool append;
 
   SetPushersRequest({
-    this.lang,
-    this.device_display_name,
-    this.app_display_name,
-    this.app_id,
-    this.kind,
-    this.pushkey,
-    this.data,
+    @required this.lang,
+    @required this.device_display_name,
+    @required this.app_display_name,
+    @required this.app_id,
+    @required this.kind,
+    @required this.pushkey,
+    @required this.data,
     this.profile_tag,
     this.append,
   });