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 
Ah, https://github.com/jashkenas/underscore/blob/master/underscore.js#L1337

I'm assuming this is because Marionette is limited to 1.6?