[Enhance]: Update .gitignore (open-mmlab#2217)

Author: Xiangxu-0103

.gitignore

@@ -132,5 +132,5 @@ data/sunrgbd/OFFICIAL_SUNRGBD/
 *.ply
 
 # Waymo evaluation
-mmdet3d/core/evaluation/waymo_utils/compute_detection_metrics_main
-mmdet3d/core/evaluation/waymo_utils/compute_detection_let_metrics_main
+mmdet3d/evaluation/functional/waymo_utils/compute_detection_metrics_main
+mmdet3d/evaluation/functional/waymo_utils/compute_detection_let_metrics_main