update docs/uniCloud/cf-database.md.

docs/uniCloud/cf-database.md

@@ -3166,6 +3166,7 @@ let res = await db.collection('orders').aggregate()
     "_id": 4,
     "title": "novel 1",
     "author": "author 1",
+    "time": 1564456048486,
     "category": "novel",
     "stock": 10,
     "book": "novel 1",