minor symfony#3801 [Cookbook][Form] Fixed Typo & missing word. (ahsio)

This PR was merged into the 2.3 branch.

Discussion
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[Cookbook][Form] Fixed Typo & missing word.

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all (or 2.3+)
| Fixed tickets |

Commits
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cc0846b add missing 's' for plural.
b140a70 Fix typo.

Author: weaverryan

cookbook/form/form_collections.rst

@@ -653,12 +653,12 @@ the relationship between the removed ``Tag`` and ``Task`` object.
     work to ensure that the relationship between the ``Task`` and the removed
     ``Tag`` is properly removed.
 
-    In Doctrine, you have two side of the relationship: the owning side and the
-    inverse side. Normally in this case you'll have a many-to-many relation
+    In Doctrine, you have two sides of the relationship: the owning side and the
+    inverse side. Normally in this case you'll have a many-to-many relationship
     and the deleted tags will disappear and persist correctly (adding new
     tags also works effortlessly).
 
-    But if you have an one-to-many relation or a many-to-many with a
+    But if you have a one-to-many relationship or a many-to-many relationship with a
     ``mappedBy`` on the Task entity (meaning Task is the "inverse" side),
     you'll need to do more work for the removed tags to persist correctly.