Update Changelog

Author: ahangarha

CHANGELOG.md

@@ -11,10 +11,11 @@ _Please add entries here for your pull requests that are not yet released._
 
 ### Breaking Changes
 - Remove support & testing for Webpacker 3/4.
-- Add support & testing for Shakapacker v6
+- Add support & testing for Shakapacker
 - Requires separate compilations for server & client bundles (see [Webpack config](https://github.com/reactjs/react-rails/tree/master/test/dummy/config/webpack))
 - Replaces WebpackManifestContainer, which searched for assets in the webpack manifest, with SeparateServerBundleContainer, which expects a single server bundle file & does not use the webpack manifest at all.
 - All in one PR! #1274
+- Drop Shakapacker 6 support in favor of Shakapacker 7 #1285
 
 #### Changed
 - The `react:component` generator now generates a function component by default #1271