Update Button to be made of Material

sky/examples/stocks-fn/stockarrow.dart

Index: sky/examples/stocks-fn/stockarrow.dart
diff --git a/sky/examples/stocks-fn/stockarrow.dart b/sky/examples/stocks-fn/stockarrow.dart
index 82e52815d2ea57b1d7763f6a0a54933d5c15e9cb..63cebf5502f2e4cd7bb95868459b8d86e2239ace 100644
--- a/sky/examples/stocks-fn/stockarrow.dart
+++ b/sky/examples/stocks-fn/stockarrow.dart
@@ -74,11 +74,11 @@ class StockArrow extends Component {
 
     return new Container(
       inlineStyle: 'border-color: $border',
-      style: _style,
+      styles: [_style],
       children: [
         new Container(
           inlineStyle: 'border-$type-color: $border',
-          style: up ? _upStyle : _downStyle
+          styles: [up ? _upStyle : _downStyle]
         )
       ]
     );