Please update the built-in React to 16.3 or higher

[JoshuaKGoldberg]

Following #564: you're React.Core.3.3.0 is on 16.0.

React.NET/src/React.Core/package.json

Line 15 in 6f6ae01

"react": "~16.0.0",

React 16.3 added React.createRef (which I happen to rely on) and generally newer versions have bug fixes, API improvements, etc.

[dustinsoftware]

Done