minor #3638 [#3116] Fixing wrong table name - singular is used elsewhere (weaverryan)

This PR was merged into the 2.3 branch.

Discussion
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[#3116] Fixing wrong table name - singular is used elsewhere

See #3116. It seems like there's a preference towards singular names, so this fixes the wrong table name, while keeping everything singular.

| Q             | A
| ------------- | ---
| Doc fix?   | yes
| New docs?  | no
| Applies to  |  2.3
| Fixed tickets | no

Thanks!

Commits
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7089d97 [#3116] Fixing wrong table name - singular is used elsewhere

Author: weaverryan

cookbook/security/entity_provider.rst

@@ -629,7 +629,7 @@ of the application::
     use Doctrine\ORM\Mapping as ORM;
 
     /**
-     * @ORM\Table(name="acme_roles")
+     * @ORM\Table(name="acme_role")
      * @ORM\Entity()
      */
     class Role implements RoleInterface