Fix sort_child_properties_last example

The GOOD example both violated the lint and did not correspond to the same layout as the BAD example.
diff --git a/lib/src/rules/sort_child_properties_last.dart b/lib/src/rules/sort_child_properties_last.dart
index 36c3084..8635112 100644
--- a/lib/src/rules/sort_child_properties_last.dart
+++ b/lib/src/rules/sort_child_properties_last.dart
@@ -52,8 +52,13 @@
     title: Text(widget.title),
   ),
   body: Center(
-    mainAxisAlignment: MainAxisAlignment.center,
+    floatingActionButton: FloatingActionButton(
+      onPressed: _incrementCounter,
+      tooltip: 'Increment',
+      child: Icon(Icons.add),
+    ),
     child: Column(
+      mainAxisAlignment: MainAxisAlignment.center,
       children: <Widget>[
         Text(
           'You have pushed the button this many times:',
@@ -64,11 +69,6 @@
          ),
       ],
     ),
-    floatingActionButton: FloatingActionButton(
-      onPressed: _incrementCounter,
-      tooltip: 'Increment',
-      child: Icon(Icons.add),
-    ),
   ),
 );
 ```