minor #14708 Replace unavailable dependency in Symfony 4 (sebpacz)

This PR was merged into the 4.4 branch.

Discussion
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Replace unavailable dependency in Symfony 4

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Commits
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1c0c7ae Replace unavailable dependency in Symfony 4

Author: OskarStark

setup/unstable_versions.rst

@@ -68,7 +68,7 @@ Symfony version has deprecated some of its features.
         $ cd projects/my_project/
         $ git checkout -b testing_new_symfony
         # ... update composer.json configuration
-        $ composer update symfony/symfony
+        $ composer update "symfony/*"
 
         # ... after testing the new Symfony version
         $ git checkout master