title: Material-UI DataGrid Width Issue
body: <p>Is it possible to get the DataGrid to only be the width of the rows without setting a containing div width?</p>
  <p>I have tried <code>disableExtendRowFullWidth={true}</code> to help, but this only does the rows. The containing DataGrid is still full wide.</p>
  <p>Here's my current code example - <a href="https://codesandbox.io/s/material-ui-issue-forked-j720c?file=/src/Demo.js" rel="nofollow noreferrer">https://codesandbox.io/s/material-ui-issue-forked-j720c?file=/src/Demo.js</a></p>