Update guard_authentication.rst

Typo

Author: ThomasLandauer

security/guard_authentication.rst

@@ -49,7 +49,7 @@ Don't forget to generate and execute the migration:
     $ php bin/console make:migration
     $ php bin/console doctrine:migrations:migrate
 
-Next, configure your "user provider" to use this new `apiKey`property:
+Next, configure your "user provider" to use this new `apiKey` property:
 
 .. configuration-block::
 
@@ -106,7 +106,6 @@ Next, configure your "user provider" to use this new `apiKey`property:
             // ...
         ]);
 
-
 Step 2) Create the Authenticator Class
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