fix flake8 error

tools/test.py

@@ -6,7 +6,7 @@ from mmcv.runner import load_checkpoint, parallel_test, obj_from_dict
 
 from mmdet import datasets
 from mmdet.core import scatter, MMDataParallel, results2json, coco_eval
-from mmdet.datasets.loader import collate, build_dataloader
+from mmdet.datasets import collate, build_dataloader
 from mmdet.models import build_detector, detectors
 
 

tools/train.py

@@ -13,7 +13,7 @@ from mmdet import datasets, __version__
 from mmdet.core import (init_dist, DistOptimizerHook, DistSamplerSeedHook,
                         MMDataParallel, MMDistributedDataParallel,
                         CocoDistEvalRecallHook, CocoDistEvalmAPHook)
-from mmdet.datasets.loader import build_dataloader
+from mmdet.datasets import build_dataloader
 from mmdet.models import build_detector, RPN