default layout name fix in form.php

Update form.php

for more accurately IDE autocompletion

In your form view https://github.com/schmunk42/yii2-giiant/blob/master/src/generators/crud/default/views/_form.php:27 you use yii\bootstrap\ActiveForm, which support only 3 kind of layout: ['default', 'horizontal', 'inline'].
Then if we chek vertical layout - we get error:
yii\base\InvalidConfigException: Invalid layout type: vertical in /home/mix/www/chaos/vendor/yiisoft/yii2-bootstrap/ActiveForm.php:92

Merge branch 'peter-vanpoucke-patch-1' of https://github.com/gtv-telecom-bvba/yii2-giiant into gtv-telecom-bvba-peter-vanpoucke-patch-1

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Conflicts:
	src/generators/crud/providers/extensions/EditableProvider.php