Added Component.json

Hi! I've added a component.json, so that expect.js can be installed via component super-simply. expect.js is already in the component.io registry, but it's missing the component.json definition. 

If you would like to add component(1) support, feel free to merge this!
If you have concerns, you could let me know and we could discuss. 

Thanks for making expect! I like it, and my team rocks it. :)

-Milan