Fixed "out_indices" and "out_features" fields in config

Fixed error where these fields were previously being stored to JSON incorrectly with underscore prefix as "_out_indices" and "_out_features". They should be stored as "out_indices" and "out_features" for proper loading of PVTv2 as a backbone.

config.json

@@ -1,11 +1,11 @@
 {
   "_name_or_path": "FoamoftheSea/pvt_v2_b1",
-  "_out_features": [
+  "out_features": [
     "stage2",
     "stage3",
     "stage4"
   ],
-  "_out_indices": [
+  "out_indices": [
     1,
     2,
     3