minor symfony#12077 Remove wrong backslash (OskarStark)

This PR was merged into the 3.4 branch.

Discussion
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Remove wrong backslash

Commits
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e8b9e9f Remove wrong backslash

Author: OskarStark

reference/configuration/twig.rst

@@ -111,7 +111,7 @@ called to determine the default escaping applied to the template.
 base_template_class
 ~~~~~~~~~~~~~~~~~~~
 
-**type**: ``string`` **default**: ``'Twig\\Template'``
+**type**: ``string`` **default**: ``'Twig\Template'``
 
 Twig templates are compiled into PHP classes before using them to render
 contents. This option defines the base class from which all the template classes