修改上次的bug

assignment/api/Document-文档作业.md

@@ -180,11 +180,11 @@ get /teacher/document/:documentId/content
 
 ```json
 {
-  "data": List<GroupSerializer>
+  "data": DocumentContentSerializer
 }
 ```
 
-see [**DocmentSerializer**](../../course/serializer/GroupSerializer.md) 
+see [**DocmentContentSerializer**](../serializer/DocumentContentSerializer.md) 
 
 
 ## 学生查看文档作业的成绩