Material-UI Enhanced Table: warnings in console

[AndreyMZ]

Describe the bug (required)
There are warnings in browser console.

Provide an example via Codesandbox! (required)
Use the react-table codesandbox to reproduce the issue.

Steps To Reproduce (required)
Steps to reproduce the behavior:

1. Go to https://react-table.js.org/examples/ui
2. Scroll down to Material-UI Enhanced Table
3. Click on Open in CodeSandbox
4. Click Console

Expected behavior (Recommended)
No warnings.

Screenshots

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Vivaldi (chromium-based)
• Version: 3.0.1874.23

[tannerlinsley]

This is an issue for MUI, not react-table. If it's a problem with the example, then I will accept a PR to update the example. Thanks!