Add missing packages in Babel section

Add missing packages in Babel section of the migration guide

Author: afdev82

docs/switch_from_webpacker.md

@@ -93,15 +93,15 @@ yarn remove @rails/webpacker webpack-dev-server
 
 ```sh
 # From the CLI, add babel presets
-yarn add @babel/core @babel/preset-env
+yarn add @babel/core @babel/preset-env babel-loader
 ```
 
 2. Configure Babel
 
 ```diff
 // In package.json, add
 + "babel": {
-+   "presets": ["@babel/env"]
++   "presets": ["@babel/preset-env"]
 + }
 ```