Update Message model

Author: JoshLipan

src/main/java/cn/jpush/api/push/model/Message.java

@@ -60,7 +60,7 @@ public JsonElement toJSON() {
         }
 
         JsonObject extrasObject = null;
-        if (null != extras || null != numberExtras || null != booleanExtras) {
+        if (null != extras || null != numberExtras || null != booleanExtras || null != jsonExtras){
             extrasObject = new JsonObject();
         }