onContextMenu PropType is missing

browser/components/MarkdownPreview.js

@@ -574,6 +574,7 @@ MarkdownPreview.propTypes = {
   onDoubleClick: PropTypes.func,
   onMouseUp: PropTypes.func,
   onMouseDown: PropTypes.func,
+  onContextMenu: PropTypes.func,
   className: PropTypes.string,
   value: PropTypes.string,
   showCopyNotification: PropTypes.bool,