Adding .sync method fixes #71

First time in my life doing CoffeeScript. I haven't broken any tests in the spec, but neither did I create new ones. I don't know TDD.

![post-11251-i-have-no-idea-what-i-am-doing-1qpa](https://cloud.githubusercontent.com/assets/364033/3004073/19e91e7a-dd74-11e3-95c4-b143e1b2764e.gif)

Here you should use double quotes and string interpolation:

```ruby
@element.querySelectorAll ".#{@config.boxClass}:not(.#{@config.animateClass})"
```