Update then statement in StatMainCard's onPressed callback

The onPressed callback of StatMainCard's RaisedButton now has a then statement with a more explicit syntax. The getStatistic method of the state object is still being called after the user taps the button.

lib/views/home/new_statistic/new_statistic.dart

@@ -233,7 +233,9 @@ class StatMainCard extends StatelessWidget {
               'label': statistic.label,
               'title': statistic.title,
               'marked': statistic.marked,
-            }).then((value) => state.getStatistic())
+            }).then(
+              (value) => state.getStatistic(),
+            )
           : null,
       child: Padding(
         padding: const EdgeInsets.all(4.0),