Merge pull request #14 from collinjackson/center_hello_world

Center the hello world text so it isn’t covered up by the status bar

R=hixie

sky/sdk/example/hello_world/lib/main.dart

@@ -6,7 +6,7 @@ import 'package:sky/widgets/basic.dart';
 
 class HelloWorldApp extends App {
   Widget build() {
-    return new Text('Hello, world!');
+    return new Center(child: new Text('Hello, world!'));
   }
 }