bug #12975 [Docs] fix annotations (SirDomin)

This PR was merged into the 1.9 branch.

Discussion
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| Q               | A
| --------------- | -----
| Branch?         | 1.9,
| Bug fix?        | no
| New feature?    | no
| BC breaks?      | no
| Deprecations?   | no
| Related tickets |
| License         | MIT

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Commits
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b1b4690 [Docs] fix annotations

docs/performance/database-indexes.rst

@@ -11,7 +11,7 @@ In this file, add indexes attribute into the table configuration:
 
 .. code-block:: php
 
-    `@ORM\Table(name="customer", indexes={@ORM\Index(name="created_at_index", fields={"created_at"})})`.
+    `@ORM\Table(name="customer", indexes={@ORM\Index(name="created_at_index", columns={"created_at"})})`.
 
 Your class should now look like this:
 
@@ -28,7 +28,7 @@ Your class should now look like this:
 
     /**
      * @ORM\Entity
-     * @ORM\Table(name="customer",indexes={@Index(name="created_at_index", fields={"created_at"})})
+     * @ORM\Table(name="customer",indexes={@ORM\Index(name="created_at_index", columns={"created_at"})})
      */
     class Customer extends BaseCustomer
     {