Deps change

[muntact]

Hey, (Thanks for the library)

I'm running into some weird issues, because i'm consuming this module via JSPM, but it looks like this package has a couple of dep changes that could be made and would still be valid for everyone.

• Proptypes should probably be a real dependency as it doesn't actually get shaken out.
  https://github.com/facebook/prop-types#how-to-depend-on-this-package
  Though this feels a bit weird when React is a peer dependency anyway 😄.

• The peer dep on react could be upstreamed to include the 16.x range. (As it totally works on react@^16.4.0 as well 😃.