Docs: Update status of Object Rest/Spread proposal

Author: jpaquim

packages/react-scripts/template/README.md

@@ -211,7 +211,7 @@ In addition to [ES6](https://github.com/lukehoban/es6features) syntax features,
 
 * [Exponentiation Operator](https://github.com/rwaldron/exponentiation-operator) (ES2016).
 * [Async/await](https://github.com/tc39/ecmascript-asyncawait) (ES2017).
-* [Object Rest/Spread Properties](https://github.com/sebmarkbage/ecmascript-rest-spread) (stage 3 proposal).
+* [Object Rest/Spread Properties](https://github.com/tc39/proposal-object-rest-spread) (ES2018).
 * [Dynamic import()](https://github.com/tc39/proposal-dynamic-import) (stage 3 proposal)
 * [Class Fields and Static Properties](https://github.com/tc39/proposal-class-public-fields) (part of stage 3 proposal).
 * [JSX](https://facebook.github.io/react/docs/introducing-jsx.html) and [Flow](https://flowtype.org/) syntax.