Fix where types is using react.PropTypes instead of prop-types.PropTypes. (#115)

Author: mastrauckas

src/types.js

@@ -1,4 +1,4 @@
-import { PropTypes } from 'react';
+import PropTypes from 'prop-types';
 
 export const ColumnSizeType = PropTypes.oneOfType([PropTypes.number, PropTypes.bool]);
 export const ViewportSizeType = PropTypes.oneOf(['xs', 'sm', 'md', 'lg']);