minor #13859 fix typo (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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fix typo

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Commits
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7f06f20 fix typo

Author: javiereguiluz

frontend/encore/simple-example.rst

@@ -50,7 +50,7 @@ of your project. It already holds the basic config you need:
 
     // ...
 
-They *key* part is ``addEntry()``: this tells Encore to load the ``assets/js/app.js``
+The *key* part is ``addEntry()``: this tells Encore to load the ``assets/js/app.js``
 file and follow *all* of the ``require()`` statements. It will then package everything
 together and - thanks to the first ``app`` argument - output final ``app.js`` and
 ``app.css`` files into the ``web/build`` directory.