Update dependencies, remove @babel/plugin-proposal-class-properties (#3225)

* Improve upgrade docs

* Update dependencies

'@babel/plugin-proposal-class-properties seems included in the preset-env

* Update v6_upgrade.md

Author: justin808

docs/v6_upgrade.md

@@ -107,7 +107,9 @@ Example going to a specific version:
 
 18. Try running `RAILS_ENV=production bin/rails assets:precompile`. If all goes well, don't forget to clean the generated assets with `bin/rails assets:clobber`.
 
-19. Try your app!
+19. Run `yarn add webpack-dev-server` if those are not already in your dev dependencies. Make sure you're using v4+.
+
+20. Try your app!
 
 ## Examples of v5 to v6
 

package.json

@@ -13,7 +13,6 @@
   },
   "dependencies": {
     "@babel/core": "^7.15.5",
-    "@babel/plugin-proposal-class-properties": "^7.14.5",
     "@babel/plugin-transform-runtime": "^7.15.0",
     "@babel/preset-env": "^7.15.6",
     "@babel/runtime": "^7.15.4",

package/babel/preset.js

@@ -42,7 +42,6 @@ module.exports = function config(api) {
       ]
     ].filter(Boolean),
     plugins: [
-      ['@babel/plugin-proposal-class-properties', { loose: true }],
       ['@babel/plugin-transform-runtime', { helpers: false }],
       isProductionEnv &&
         moduleExists('babel-plugin-transform-react-remove-prop-types') && [