React 15.5 moved PropTypes to separate package

[kengorab]

In versions of React newer than 15.5, PropTypes is no longer exported and has been moved to the prop-types package. Details here: https://reactjs.org/blog/2017/09/26/react-v16.0.html#packaging

The fix for this should be simple: add the prop-types package as a dependency (as is recommended by their docs) and do

import PropTypes from 'prop-types'

rather than

import { PropTypes } from 'react'