Fix invalid ItemView example in docs

Looks like this was changed acknowledge the `underscore@1.7` template changes, however it nolonger passes the `variable: 'args'`

(90% sure) this should work in any version of underscore >= 1 
What's the null here? The underscore docs don't have this:
```js
_.template("Using 'with': <%= data.answer %>", {variable: 'data'})({answer: 'no'});
=> "Using 'with': no"
```