Fixes a bug in gson's deserialization feature (apache#5099)

Author: goodjava

dubbo-rpc/dubbo-rpc-dubbo/src/main/java/org/apache/dubbo/rpc/protocol/dubbo/DecodeableRpcResult.java

@@ -141,7 +141,7 @@ private void handleValue(ObjectInput in) throws IOException {
 
     private void handleException(ObjectInput in) throws IOException {
         try {
-            Object obj = in.readObject();
+            Object obj = in.readObject(Throwable.class);
             if (!(obj instanceof Throwable)) {
                 throw new IOException("Response data error, expect Throwable, but get " + obj);
             }

dubbo-serialization/dubbo-serialization-gson/src/main/java/org/apache/dubbo/common/serialize/gson/GsonJsonObjectInput.java

@@ -90,7 +90,7 @@ public byte[] readBytes() throws IOException {
     @Override
     public Object readObject() throws IOException, ClassNotFoundException {
         String json = readLine();
-        return gson.fromJson(json, String.class);
+        return gson.fromJson(json, Object.class);
     }
 
     @Override