minor #13537 typo date (zairigimad)

This PR was submitted for the 5.0 branch but it was merged into the 3.4 branch instead.

Discussion
----------

typo date

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/roadmap for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `master` for features of unreleased versions).

-->

Commits
-------

f969015 typo

Author: javiereguiluz

contributing/code/license.rst

@@ -5,7 +5,7 @@ Symfony Code License
 
 Symfony code is released under `the MIT license`_:
 
-Copyright (c) 2004-2019 Fabien Potencier
+Copyright (c) 2004-2020 Fabien Potencier
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal