bug #6608 deprecated 'datettime' Form Type (dsmink)

This PR was submitted for the 3.0 branch but it was merged into the 2.8 branch instead (closes #6608).

Discussion
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deprecated 'datettime' Form Type

'datettime' to DateTimeType::class

Commits
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cae7a80 deprecated 'datettime' Form Type

Author: wouterj

reference/forms/types/datetime.rst

@@ -87,14 +87,18 @@ If your widget option is set to ``choice``, then this field will be represented
 as a series of ``select`` boxes. When the placeholder value is a string,
 it will be used as the **blank value** of all select boxes::
 
-    $builder->add('startDateTime', 'datetime', array(
+    use Symfony\Component\Form\Extension\Core\Type\DateTimeType;
+    
+    $builder->add('startDateTime', DateTimeType::class, array(
         'placeholder' => 'Select a value',
     ));
 
 Alternatively, you can use an array that configures different placeholder
 values for the year, month, day, hour, minute and second fields::
 
-    $builder->add('startDateTime', 'datetime', array(
+    use Symfony\Component\Form\Extension\Core\Type\DateTimeType;
+    
+    $builder->add('startDateTime', DateTimeType::class, array(
         'placeholder' => array(
             'year' => 'Year', 'month' => 'Month', 'day' => 'Day',
             'hour' => 'Hour', 'minute' => 'Minute', 'second' => 'Second',