Do not exclude node_modules

See [Enable babel-preset-env for node_modules that target newer Node versions](facebook/create-react-app#1125)
See [Create React App 2.0: "You can now use packages written for latest Node versions without breaking the build"](https://reactjs.org/blog/2018/10/01/create-react-app-v2.html)
See ["If you have to exclude node_modules/, how do you get babel to polyfill/transform code in 3rd party code?"](webpack/webpack#6544 (comment))
See [Compile dependencies with babel-preset-env](facebook/create-react-app#3776)

examples/Bootstrap4/webpack.config.js

@@ -18,7 +18,7 @@ module.exports = {
 
   module: {
     rules: [
-      { test: /\.jsx?$/, exclude: /node_modules/, loader: 'babel-loader' },
+      { test: /\.jsx?$/, loader: 'babel-loader' },
       { test: /\.js$/, loader: 'source-map-loader' },
       { test: /\.html$/, loader: 'file-loader', options: {name: '[path][name].[ext]'} },
       {