minor #4819 Removed a leftover comma in security config sample (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
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Removed a leftover comma in security config sample

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | -

Commits
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83be144 Removed a leftover comma in security config sample

Author: wouterj

book/security.rst

@@ -295,7 +295,7 @@ provider, but it's better to think of it as an "in configuration" provider:
                     memory:
                         users:
                             ryan:
-                                password: ryanpass,
+                                password: ryanpass
                                 roles: 'ROLE_USER'
                             admin:
                                 password: kitten