Progress bar should handle the 0% case

Created by: stubbornella

I noticed that the progress bar doesn't handle the 0% progress case gracefully. The text is white on a light gray background and touches the edge of the outer bar.

http://jsbin.com/waver/1/

Perhaps I've not set some necessary variable or I was meant to add a class?

I ended up fixing it like this: (though it feels a bit clunky)

.progress-bar.progress-bar-zero {
  color: $text-color;
  min-width: 3%;
  background: transparent;
  box-shadow: none;
}

Happy to put together a pull request if this seems useful.