Fix a minor typo in the `update()` docs

docs/09.6-update.md

@@ -40,7 +40,7 @@ var newData = extend(myData, {
 
 While this is fairly performant (since it only shallow copies `log n` objects and reuses the rest), it's a big pain to write. Look at all the repetition! This is not only annoying, but also provides a large surface area for bugs.
 
-`update() provides simple syntactic sugar around this pattern to make writing this code easier. This code becomes:
+`update()` provides simple syntactic sugar around this pattern to make writing this code easier. This code becomes:
 
 ```javascript
 var newData = React.addons.update(myData, {