Update marionette.itemview.md

[bafolts]

The old example for 'variable' in the documentation did not work for me. The 'settings' argument is the 2nd or 3rd argument of the _.template function. The model is then passed in as a parameter to the then generated template function. I attempted to update the documentation to reflect this.

[coveralls]

Coverage remained the same when pulling 9319c27 on bafolts:patch-1 into f65e4cd on marionettejs:master.

[samccone]

@bafolts are you on Underscore 1.7 by chance?

[bafolts]

That is the one. Sorry, most likely could have included that with the pull request.

[samccone]

Underscore 1.7 is not supported in Marionette due to numerous breaking changes in that version.

ref #1833
ref jashkenas/underscore#1805

For now just use 1.6

[jamesplease]

Thanks for the report @bafolts. As @samccone pointed out we're stuck on 1.6 due to the breaking changes in 1.7. We try to keep Marionette backwards compatible, so it might be some time before we can make the change to support 1.7.

[bafolts]

Removing the specific reference to the "variable" settings for underscore could help for now. That was the only misleading part and really isn't related to Marionette as it is underscore. All that really matters in Marionette is that I can call _.template from the function passed in for 'template'.

[jamesplease]

I admit I haven't had the time to look at the issue of 1.7 in Marionette too much, but if a documentation change could help people out then I think we should think more about it.

[coveralls]

Coverage remained the same when pulling 9319c27 on bafolts:patch-1 into f65e4cd on marionettejs:master.

[coveralls]

Coverage remained the same when pulling 6f52fec on bafolts:patch-1 into f65e4cd on marionettejs:master.

[samccone]

manually merged

thanks!