Fix note formatting (#10966)

docs/reference-react.md

@@ -71,7 +71,7 @@ See the [React.Component API Reference](/docs/react-component.html) for a list o
 If your React component's `render()` function renders the same result given the same props and state, you can use `React.PureComponent` for a performance boost in some cases.
 
 > Note
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 > `React.PureComponent`'s `shouldComponentUpdate()` only shallowly compares the objects. If these contain complex data structures, it may produce false-negatives for deeper differences. Only extend `PureComponent` when you expect to have simple props and state, or use [`forceUpdate()`](/docs/react-component.html#forceupdate) when you know deep data structures have changed. Or, consider using [immutable objects](https://facebook.github.io/immutable-js/) to facilitate fast comparisons of nested data.
 >
 > Furthermore, `React.PureComponent`'s `shouldComponentUpdate()` skips prop updates for the whole component subtree. Make sure all the children components are also "pure".