Unable to style spinner or progress-bar-percent with css modules

[outdooricon]

Thanks for this project, I love it! I'm having an issue styling the bar as I'm using React-Boilerplate and all css is built using css modules. So, all styling is single-level and I currently have no way of of modifying the styles of the children inside of the progress bar, only the outer div.

I propose exposing spinnerClassName and percentBarClassName as additional props so that I can set specific classes on both of them.