title: React prop validation for date objects
body: <p><strong>What is the currently preferred way to validate a <code>Date</code> prop in react?</strong></p>
  
  <p>Right now I'm using: <code>React.PropTypes.object</code></p>
  
  <p>This, however, is now failing the <a href="https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/forbid-prop-types.md">forbid-prop-types</a> lint rule. Should I use a <code>shape</code> or is there some better way?</p>