minor #13862 update sass-loader version printed in symfony 5.1 (nabbisen)

This PR was submitted for the 5.1 branch but it was merged into the 3.4 branch instead.

Discussion
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update sass-loader version printed in symfony 5.1

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Commits
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473fdc2 update sass-loader version printed in symfony 5.1

Author: javiereguiluz

frontend/encore/simple-example.rst

@@ -306,14 +306,14 @@ Encore. When you do, you'll see an error!
 .. code-block:: terminal
 
     >   Error: Install sass-loader & node-sass to use enableSassLoader()
-    >     yarn add sass-loader@^7.0.1 node-sass --dev
+    >     yarn add sass-loader@^8.0.0 node-sass --dev
 
 Encore supports many features. But, instead of forcing all of them on you, when
 you need a feature, Encore will tell you what you need to install. Run:
 
 .. code-block:: terminal
 
-    $ yarn add sass-loader@^7.0.1 node-sass --dev
+    $ yarn add sass-loader@^8.0.0 node-sass --dev
     $ yarn encore dev --watch
 
 Your app now supports Sass. Encore also supports LESS and Stylus. See