Fix minor typo in update $push directive

docs/09.6-update.md

@@ -45,7 +45,7 @@ While this is fairly performant (since it only shallow copies `log n` objects an
 ```javascript
 var newData = React.addons.update(myData, {
   x: {y: {z: {$set: 7}}},
-  a: {b: {$push: [7]}}
+  a: {b: {$push: [9]}}
 });
 ```