Fix typo (#7909)

docs/ref-01-top-level-api.md

@@ -216,4 +216,4 @@ If you call `ReactDOM.render()` on a node that already has this server-rendered
 string renderToStaticMarkup(ReactElement element)
 ```
 
-Similar to `renderToString`, except this doesn't create extra DOM attributes such as `data-react-id`, that React uses internally. This is useful if you want to use React as a simple static page generator, as stripping away the extra attributes can save lots of bytes.
+Similar to `renderToString`, except this doesn't create extra DOM attributes such as `data-reactid`, that React uses internally. This is useful if you want to use React as a simple static page generator, as stripping away the extra attributes can save lots of bytes.