Mismatch between compile-time and runtime type checking for columns.field

[hill-giant]

Describe the bug
Support for passing an array to the 'field' attribute of a column was previously added in #417 to allow the selection of keys with full-stops. Although the the type of the field was updated in the type declaration file, prop-types.js was not updated to reflect these changes, resulting in runtime errors.

To Reproduce
Steps to reproduce the behavior:

1. Pass a string array to a column field.
2. Run in development.
3. Go to dev console.
4. See error.

Expected behavior
Column fields of type string array should not result in runtime errors.

Screenshots

Demo

• CodeSandbox

Solution
Update prop-types.js to allow both type string array and type string for columns.field.

This is an easy fix, which I will gladly put up for review.