Update react-component.html for React 16.2's improved fragment support

[edmorley]

Hi!

React 16.2.0 improved support for fragments, and #392 added some documentation in this repo for them.

However I've spotted another reference to fragments that is still using the array syntax - that I think should probably be updated too?
https://reactjs.org/docs/react-component.html#fragments

[clemmy]

Yes, documentation updates would be very welcome PRs. In the past, the array syntax was also called fragments, so there's a bit of mismatch in the documentation.