update sniper config (#4429)

configs/sniper/faster_rcnn_r50_fpn_1x_visdrone.yml

 _BASE_: [
   '../datasets/coco_detection.yml',
   '../runtime.yml',
-  '_base_/optimizer_1x.yml',
-  '_base_/faster_rcnn_r50_fpn.yml',
-  '_base_/faster_fpn_reader.yml',
+  '../faster_rcnn/_base_/optimizer_1x.yml',
+  '../faster_rcnn/_base_/faster_rcnn_r50_fpn.yml',
+  '../faster_rcnn/_base_/faster_fpn_reader.yml',
 ]
 weights: output/faster_rcnn_r50_fpn_1x_visdrone/model_final
 

configs/sniper/ppyolo_r50vd_dcn_1x_visdrone.yml

 _BASE_: [
   '../datasets/coco_detection.yml',
   '../runtime.yml',
-  './_base_/ppyolo_r50vd_dcn.yml',
-  './_base_/optimizer_1x.yml',
-  './_base_/ppyolo_reader.yml',
+  '../ppyolo/_base_/ppyolo_r50vd_dcn.yml',
+  '../ppyolo/_base_/optimizer_1x.yml',
+  '../ppyolo/_base_/ppyolo_reader.yml',
 ]
 
 snapshot_epoch: 8