Add underscore to package.json

[eguneys]

I installed this as an ember-cli add on npm install and it gives me Error: _ is undefined.

[locks]

It's in the bower.json, since it's a front-side dependency: https://github.com/locks/ember-data-hal-adapter/blob/master/bower.json#L25 I think the actual problem is that I'm not including the underscore files into the Brocfile, so you might have to do it manually. I'll see about doing that, or removing the underscore dependency.

[eguneys]

I've made some changes, I can't do a pull request, why?