Fix issue symfony#3442

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3
| Fixed tickets | symfony#3442

Author: ifdattic

cookbook/form/form_collections.rst

@@ -20,7 +20,7 @@ that Task, right inside the same form.
     including the ``ManyToMany`` association mapping definition on the Task's
     ``tags`` property.
 
-Let's start there: suppose that each ``Task`` belongs to multiple ``Tags``
+Let's start there: suppose that each ``Task`` belongs to multiple ``Tag``
 objects. Start by creating a simple ``Task`` class::
 
     // src/Acme/TaskBundle/Entity/Task.php