forceDisabled and classnames dependency

[calderhayes]

Hello,

Thanks for this library, it looks so simple yet feature complete.

I have one minor adjustment, I noticed that it was included in a pull request before disappearing after a refactor (I think).

It has popped up before in the issues.

Basically I require an override on the disabled property when processing the form data asynchronously. I don't want the user to click the submit button while this is going on.

I also ran into an issue where classnames was required, but not in the npm list of dependencies causing the unit tests to break.

Thanks,

Calder

[coveralls]

Coverage remained the same at 100.0% when pulling 4d1e92a on calderhayes:master into aa2b38c on Lesha-spr:master.