fix wrong activation function for multi-label classification

config.json

@@ -47,6 +47,7 @@
     "female": 8,
     "homosexual_gay_or_lesbian": 9
   },
+  "problem_type": "multi_label_classification",
   "layer_norm_eps": 1e-05,
   "max_position_embeddings": 514,
   "model_type": "roberta",