minor #4185 [Components][Form] Fixed typo in datetime type reference (althaus)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4185).

Discussion
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[Components][Form] Fixed typo in datetime type reference

Fixed "the the" typo.

Commits
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7c42e4b Update datetime.rst
d556309 Update datetime.rst

Author: weaverryan

reference/forms/types/datetime.rst

@@ -74,7 +74,7 @@ format
 
 **type**: ``string`` **default**: ``Symfony\Component\Form\Extension\Core\Type\DateTimeType::HTML5_FORMAT``
 
-If the ``widget`` option is set to ``single_text``, this option specifies the
+If the ``widget`` option is set to ``single_text``, this option specifies
 the format of the input, i.e. how Symfony will interpret the given input
 as a datetime string. It defaults to the `RFC 3339`_ format which is used
 by the HTML5 ``datetime`` field. Keeping the default value will cause the