Update README.md (#983)

Author: 0xdevalias

README.md

@@ -8,7 +8,7 @@
 
 React-Rails is a flexible tool to use [React](http://facebook.github.io/react/) with Rails. The benefits:
 * Automatically renders React server-side and client-side
-* Supports Webpacker 3.x, 2.x, 1.1+
+* Supports Webpacker 4.x, 3.x, 2.x, 1.1+
 * Supports Sprockets 4.x, 3.x, 2.x
 * Lets you use [JSX](http://facebook.github.io/react/docs/jsx-in-depth.html), [ES6](http://es6-features.org/), [TypeScript](https://www.typescriptlang.org/), [CoffeeScript](http://coffeescript.org/)