Set react and react-dom as peer dependencies

[joe-tohdjojo]

In the package.json file, we are requiring react and react-dom as a dependency but this package shouldn't bring in it's own version of react if it's meant to be used with react and react-dom already. Those packages should be declared as peer dependencies. If I understand it correctly, this should reduce our bundle size as well since we wont be importing a separate version of react and react-dom

This fix should also fix the security vulnerability in react-dom mentioned here: https://nvd.nist.gov/vuln/detail/CVE-2018-6341

[Demven]

Great proposal, @joseph-tohdjojo I'll update it today!