fix response `content-type` is not set if access without access token

Kairlec

2023-05-15 ca103731c721aae3f5f622e58c679ed5c09fd9e9

 src/main/java/com/genersoft/iot/vmp/media/zlm/dto/HookSubscribeForStreamChange.java

@@ -15,6 +15,7 @@

    private JSONObject content;

    @JSONField(format="yyyy-MM-dd HH:mm:ss")
    private Instant expires;

    @Override