[Bug]fix mmdet bc breaking (#1434)

* fix mmdet bc breaking

* fix version

tools/test.py

@@ -11,17 +11,18 @@ from mmcv.parallel import MMDataParallel, MMDistributedDataParallel
 from mmcv.runner import (get_dist_info, init_dist, load_checkpoint,
                          wrap_fp16_model)
 
+import mmdet
 from mmdet3d.apis import single_gpu_test
 from mmdet3d.datasets import build_dataloader, build_dataset
 from mmdet3d.models import build_model
 from mmdet.apis import multi_gpu_test, set_random_seed
 from mmdet.datasets import replace_ImageToTensor
 
-try:
-    # If mmdet version > 2.20.0, setup_multi_processes would be imported and
+if mmdet.__version__ > '2.23.0':
+    # If mmdet version > 2.23.0, setup_multi_processes would be imported and
     # used from mmdet instead of mmdet3d.
     from mmdet.utils import setup_multi_processes
-except ImportError:
+else:
     from mmdet3d.utils import setup_multi_processes