update: adding model type for onnx conversion

config.json

@@ -1,4 +1,5 @@
 {
+"model_type": "style_text_to_speech_2",
   "istftnet": {
     "upsample_kernel_sizes": [20, 12],
     "upsample_rates": [10, 6],
@@ -204,4 +205,4 @@
     "云": 176,
     "ᵻ": 177
   }
-}
+}