Summary:
Hi!
Just noticed an incorrect description for the `hidden` argument for `StatusBar.setHidden()` on the website, this trivial change fixes that.
FYI I followed the start procedure for the website mentioned in [CONTRIBUTING.md](https://github.com/facebook/react-native/blob/master/CONTRIBUTING.md#pull-requests), and noticed one needs to run `npm install` in the project root directory as well before starting the website. Do you want me to add that instruction as part of this PR, or as a separate PR entirely?
Closes https://github.com/facebook/react-native/pull/10735
Differential Revision: D4131223
fbshipit-source-id: b70c5ef12e72807445c51f13811537b9fa3b6b3e
