minor #3180 Fix small typo (kevin-verschaeve)

This PR was merged into the 2.x branch.

Discussion
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Fix small typo

Commits
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d48aceb Fix small typo

doc/filters/u.rst

@@ -70,7 +70,7 @@ For large strings manipulation, use the ``apply`` tag:
         $ composer req twig/string-extra
 
     Then, use the ``twig/extra-bundle`` on Symfony projects or add the extension
-    explictly on the Twig environment::
+    explicitly on the Twig environment::
 
         use Twig\Extra\String\StringExtension;