minor symfony#10305 Fix broken link to Security tutorial (bocharsky-bw)

This PR was merged into the 4.1 branch.

Discussion
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Fix broken link to Security tutorial

Affected Symfony 4 version only

Commits
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7884af4 Fix broken link to Security tutorial

Author: javiereguiluz

security.rst

@@ -1348,4 +1348,4 @@ Other Security Related Topics
 .. _`frameworkextrabundle documentation`: https://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/index.html
 .. _`HWIOAuthBundle`: https://github.com/hwi/HWIOAuthBundle
 .. _`Symfony ACL bundle`: https://github.com/symfony/acl-bundle
-.. _`Symfony Security screencast series`: https://knpuniversity.com/screencast/symfony4-security
+.. _`Symfony Security screencast series`: https://knpuniversity.com/screencast/symfony-security