Add 'add_pooling_layer=False' to ST config

sentence_bert_config.json

@@ -1,4 +1,7 @@
 {
   "max_seq_length": 512,
-  "do_lower_case": false
+  "do_lower_case": false,
+  "model_args": {
+    "add_pooling_layer": false
+  }
 }