Upgrade to seperate React prop-types library.

`propTypes` was seperated/depreciated from React as of 15.5.0:
https://facebook.github.io/react/blog/2017/04/07/react-v15.5.0.html#migrating-from-react.proptypes

src/components/UI/Sticky/Sticky.js

@@ -1,4 +1,5 @@
-import React, { Component, PropTypes } from 'react';
+import PropTypes from 'prop-types';
+import React, { Component } from 'react';
 import classnames from 'classnames';
 import { partial, without } from 'lodash';
 import styles from './Sticky.css';

src/components/UI/toast/Toast.js

@@ -1,4 +1,5 @@
-import React, { PropTypes } from 'react';
+import PropTypes from 'prop-types';
+import React from 'react';
 import { Icon } from '../index';
 import styles from './Toast.css';