fix reference to babel-preset-env in readme

Author: chrisbreiding

README.md

@@ -77,7 +77,7 @@ Object of webpack options. Just `require` in the options from your `webpack.conf
         use: [{
           loader: 'babel-loader',
           options: {
-            presets: ['babel-preset-env'],
+            presets: ['@babel/preset-env'],
           },
         }],
       },