Fixing Huboard badge on README.md

Badge should be fixed now with this pull request.

By the way, we used the huboard badges as a test to see if people liked linking their repo to a product that helps them track their work.

We built a new product, waffle.io, to provide functionality similar to huboard with the added benefit that anyone can see your board, without having to login to GitHub. As a Huboard user we'd love your feedback!