DateTime Validator use the DATETIME_FORMAT instead of the given format

[amohammad]

in the new function "valueIsValidDateTimeFormat($value)" in zend-form/src/Element/DateTime.php use the "static::DATETIME_FORMAT" instead of the given format in the form element and i get this error message " Zend\Form\Element\DateTime::getValidators expects "max" to conform to Y-m-d\TH:iP; received "2017-06-15" "

I think this line of code here should be changed to

$this->getFormat(),

Thanks.

[alirezameskin]

I have fixed the problem #170

[Kwido]

@alireza-m any progress on the requested changes?