fix cli arg parsing

Summary: fix D34540275 (https://github.com/facebookresearch/d2go/commit/d8bdc633ec66e6ce73076d027f8e777791c2e067)

Reviewed By: tglik

Differential Revision: D34662745

fbshipit-source-id: 6fd67db041fab6f5810763702e4cc3f16a08c5df

tools/train_net.py

@@ -104,4 +104,4 @@ def cli(args):
 
 
 if __name__ == "__main__":
-    cli(sys.argv)
+    cli(sys.argv[1:])