Updates veggieseasons to Dart 2.3, adds some minor UI updates (#88)

veggieseasons/lib/screens/settings.dart

@@ -139,7 +139,7 @@ class SettingsScreen extends StatelessWidget {
           return Row(
             children: [
               Text(snapshot.data?.toString() ?? ''),
-              SizedBox(width: 8.0),
+              SizedBox(width: 8),
               SettingsNavigationIndicator(),
             ],
           );