bug #5110 [Serializer] Fix class name (iamluc)

This PR was merged into the 2.7 branch.

Discussion
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[Serializer] Fix class name

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.7, master
| Fixed tickets |

CamelCaseToSnakeCaseNameConverter instead of CamelCaseToUnderscoreNameConverter

Commits
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a1f2ed7 Fix class name

components/serializer.rst

@@ -241,7 +241,7 @@ CamelCase to snake_case
 ~~~~~~~~~~~~~~~~~~~~~~~
 
 .. versionadded:: 2.7
-    The :class:`Symfony\\Component\\Serializer\\NameConverter\\CamelCaseToUnderscoreNameConverter`
+    The :class:`Symfony\\Component\\Serializer\\NameConverter\\CamelCaseToSnakeCaseNameConverter`
     interface was introduced in Symfony 2.7.
 
 In many formats, it's common to use underscores to separate words (also known