Adding wiredep block

This will help me to add backbone and its dependencies into `test/index.html` from backbone generator.

backbone generator will below config this to generated `Gruntfile.js`
```js
        wiredep: {
            test: {
                src: [
                    'test/index.html'
                ],
                options: {
                    ignorePath: '../app/'
                }
            }
        }
```