minor #1162 [Docs] [Providers] Fixed typo (ureimers)

This PR was submitted for the master branch but it was merged into the 1.2 branch instead (closes #1162).

Discussion
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[Docs] [Providers] Fixed typo

Commits
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cb279a24 [Docs] [Providers] Fixed typo

doc/providers/form.rst

@@ -17,7 +17,7 @@ Services
 
 * **form.factory**: An instance of `FormFactory
   <http://api.symfony.com/master/Symfony/Component/Form/FormFactory.html>`_,
-  that is used for build a form.
+  that is used to build a form.
 
 * **form.csrf_provider**: An instance of an implementation of the
   `CsrfProviderInterface