message: adapt "test_schema()" to GDAL 2.x
diff: @@ -130,6 +130,7 @@ fn test_schema() {
  .map(|f| (f.name(), f.field_type()))
  .collect();
  let ok_names_types: Vec<(String, OGRFieldType)> = vec!(
  + ("id", OGRFieldType::OFTString),
  ("kind", OGRFieldType::OFTString),
  ("sort_key", OGRFieldType::OFTReal),
  ("is_link", OGRFieldType::OFTString),
  