fix wrong activation function for multi-label classification

config.json

@@ -25,6 +25,7 @@
     "insult": 4,
     "identity_hate": 5
   },
+  "problem_type": "multi_label_classification",
   "layer_norm_eps": 1e-12,
   "max_position_embeddings": 512,
   "model_type": "bert",