minor symfony#8134 Fix minor typo (tobemedia)

This PR was squashed before being merged into the 3.3 branch (closes symfony#8134).

Discussion
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Fix minor typo

Commits
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6beff5e Fix minor typo

Author: xabbuh

frontend/encore/versus-assetic.rst

@@ -3,7 +3,7 @@ Encore Versus Assetic?
 
 Symfony originally shipped with support for :doc:`Assetic </assetic>`: a
 pure PHP library capable of processing, combining and minifying CSS and JavaScript
-files. And while Encore is now the recommended way or processing your assets, Assetic
+files. And while Encore is now the recommended way of processing your assets, Assetic
 still works well.
 
 So what are the differences between Assetic and Encore?