create_toy_dataset: instance indices start at 1

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/447

The first instance of each toy dataset was ignored when running cocoeval (null instance ids in the gt are not counted). See https://github.com/cocodataset/cocoapi/blob/master/PythonAPI/pycocotools/cocoeval.py#L39

Reviewed By: wat3rBro

Differential Revision: D42080839

fbshipit-source-id: df5c758ba0a858a514c6d4a3c68d659b5b7220e5

d2go/utils/testing/data_loader_helper.py

@@ -74,7 +74,7 @@ def create_toy_dataset(
             {
                 "image_id": i,
                 "category_id": i % num_classes,
-                "id": i,
+                "id": i + 1,
                 "bbox": bbox,
                 "keypoints": keypoints,
                 "area": width * height,