Fix class import typo. Issue #2.

Author: dadish

src/Field/Page/Fieldtype/FieldtypeDatetime.php

@@ -2,7 +2,7 @@
 
 namespace ProcessWire\GraphQL\Field\Page\Fieldtype;
 
-use Youshido\GraphQL\Type\Scalar\DatetimeType;
+use Youshido\GraphQL\Type\Scalar\DateTimeType;
 use ProcessWire\GraphQL\Field\Page\Fieldtype\AbstractFieldtype;
 
 class FieldtypeDatetime extends AbstractFieldtype {
@@ -12,4 +12,4 @@ public function getDefaultType()
     return new DatetimeType();
   }
 
-}
+}