minor symfony#10630 Fix typo (fishmandev)

This PR was merged into the 4.1 branch.

Discussion
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Fix typo

Commits
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f9d7c75 Fix typo

Author: javiereguiluz

security.rst

@@ -124,8 +124,8 @@ command will pre-configure this for you:
             encoders:
                 # use your user class name here
                 App\Entity\User:
-                    # bcrypt or argon21 are recommended
-                    # argon21 is more secure, but requires PHP 7.2 or the Sodium extension
+                    # bcrypt or argon2i are recommended
+                    # argon2i is more secure, but requires PHP 7.2 or the Sodium extension
                     algorithm: bcrypt
                     cost: 12