v2.9.7

Update dependencies to be more flexible.

In 2.9.6, we swapped out React.PropTypes for the dedicated prop-types package.

I realized right after publish that it made more sense to move this dependency to peerDependencies, and to loosen the version restriction to 15.x.x. This way, users can bring their own version, and NPM won't complain if theirs is a patch or minor version off.

Thanks again to @Hypnosphi for his underlying work on the prop-types conversion.

Apologies for the rapid-fire releases today!