minor #11051 Uncomment some code in the "Configuring Babel" example (Lyrkan)

This PR was merged into the 3.4 branch.

Discussion
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Uncomment some code in the "Configuring Babel" example

This PR uncomment some lines of code in the `Encore.configureBabel(...)` example based on a feedback given in symfony/webpack-encore#528 (comment).

Commits
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ec6f46b Uncomment some code in "Configuring Babel"

Author: javiereguiluz

frontend/encore/babel.rst

@@ -18,17 +18,19 @@ Need to extend the Babel configuration further? The easiest way is via
 
         .configureBabel(function(babelConfig) {
             // add additional presets
-            // babelConfig.presets.push('@babel/preset-flow');
+            babelConfig.presets.push('@babel/preset-flow');
 
             // no plugins are added by default, but you can add some
-            // babelConfig.plugins.push('styled-jsx/babel');
+            babelConfig.plugins.push('styled-jsx/babel');
         }, {
             // node_modules is not processed through Babel by default
             // but you can whitelist specific modules to process
-            // include_node_modules: ['foundation-sites']
+            include_node_modules: ['foundation-sites'],
 
-            // or completely control the exclude
-            // exclude: /bower_components/
+            // or completely control the exclude rule (note that you
+            // can't use both "include_node_modules" and "exclude" at
+            // the same time)
+            exclude: /bower_components/
         })
     ;