[ADD] padding to demo

Author: jay-k98

example/lib/presentation/samples/stacked_pie/stacked_pie_chart_sample1.dart

@@ -22,6 +22,7 @@ class _StackedPieChartSample1State extends State<StackedPieChartSample1> {
               child: StackedPieDemo(),
             ),
           ),
+          SizedBox(height: 28),
         ],
       ),
     );