Update API response to only be date, not full datetimestamp

doc/api/members.md

@@ -552,7 +552,7 @@ Example response:
   "state": "active",
   "avatar_url": "https://www.gravatar.com/avatar/c2525a7f58ae3776070e44c106c48e15?s=80&d=identicon",
   "web_url": "http://192.168.1.8:3000/root",
-  "expires_at": "2012-10-22T14:13:35Z",
+  "expires_at": "2012-10-22",
   "access_level": 40,
   "email": "john@example.com",
   "override": false